When Nicola Sturgeon took the stage on 28 March before 3,000 devotees at the Scottish National party’s spring conference in Glasgow, the SNP’s deputy leader, Stewart Hosie, introduced her as “the only party leader in the UK who people actually like ... let me just say that again, the only party leader with positive approval ratings throughout the UK”. The audience whistled, clapped and cheered, and Sturgeon, in her best Kurt Geigers and coral-pink suit, climbed up the few steps to the platform, where her already-gathered cabinet rose from their chairs and, like a well-drilled military unit, turned to greet her with their arms outstretched in applause. A screen behind them showed that the number of SNP members now stood at 102,143, a fourfold increase since September’s referendum. The SNP is now the third largest party in Britain.

This kind of choreographed triumphalism can easily go wrong – think of Neil Kinnock’s disastrous performance at the Sheffield rally in 1992 – but Sturgeon has a self-deprecatory way of talking, smiling and frowning that deflates any charge of hubris or vanity. She smiled and shook her head at the crowd’s roar as if she didn’t quite believe it, and when she reached the lectern and looked into the hall, her first words were: “What a sight!”, which in Scotland is more often an expression of disapproval than amazement.

How good it was, she began, to be in “the wonderful ‘yes’ city of Glasgow”, which had voted for independence in the referendum – unlike most of the rest of country. Never mind that Scotland “didn’t choose independence ... [theatrical pause] this time”, the party intended to make Westminster sit up and take notice. “Let us put the normal divisions of politics aside, let us come together as one country, let us seize this historic moment to shift the balance of power from the corridors of Westminster to the streets and communities of Scotland,” she said. “Let us this time vote SNP and make this nation’s voice heard like never before.”

It was a good speech – the kind of speech (as more than one observer noted) that a Labour politician in Scotland would have wanted to make and that a Scottish Labour voter would have wanted to hear. Sturgeon railed against “slash-and-burn austerity” and the “cosy consensus” that hit the poor with benefits sanctions while turning a blind eye to the tax avoidance of the super-rich. She reached out to “progressive opinion all across the UK”. She promised to stand firm against “the obscene status symbol that is a new generation of Trident nuclear weapons”. Not least, she attacked Westminster as a remote and oppressive institution – “the House of Lords has no place in a democratic society” – rather than as a decadent but relatively harmless club where some members fiddle their expenses and shout too much.

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Her strategy was plain for all to see, and yet Ed Miliband has still to find a half-persuasive answer to it. The SNP is predicted to take more than 50 of Scotland’s 59 seats – reducing Scottish Labour to single digits – and Sturgeon declared that Labour and the SNP should pass a no-confidence motion that would “lock David Cameron out of Downing Street”. If Labour failed to make that commitment, then people would conclude that Labour would rather have the Tories in power than work with the SNP. That would be the final nail in the coffin of Scottish Labour: “It really will be time to lock the doors on the branch office once and for all.” Whatever happened, she insisted, Labour could not be trusted. “If you want a Labour government to have backbone and guts, you need to elect SNP MPs to provide it for them ... you must elect SNP MPs to force Labour’s hand and keep them honest.”

Ovations interrupted the speech throughout, and not the dutiful kind that need to be wheedled from the delegates at other party conferences. The columnist Alan Watkins liked to tease pre-Blair Labour with the acronym THIGMOO (This Great Movement of Ours) – a more or less affectionate nod to the party’s sentimentalism, manifested in rituals such as joining hands on the conference stage and singing The Red Flag. The SNP now occupies that emotional space much more vigorously. With rather more reason than modern Labour, it likes to think of itself as a Great Movement as well as a party; a fervent cause with a simple objective (simpler, for example, than socialism) underpinned by the tactical opportunism common to any successful political campaign – or successful government, because it is that, too. A movement, a party and a government, then, and all three led by a woman recognised by many people in Scotland as somehow typical of themselves. Approachable, egalitarian, demotic, commonsensical, they say, as they look in the mirror.

Facebook Twitter Pinterest Sturgeon with Alex Salmond in 2007. Photograph: David Moir/Reuters

Nor, it has turned out, is her appeal confined to north of the border. After her appearance the following week on the first of the televised leaders’ debates, her name was the most Googled of all the participants. So many people living outside Scotland wanted to know if they could vote for the SNP that it was the sixth-most searched question in the UK during the debate. Her predecessor, Alex Salmond, has also enjoyed some popularity in England as a caustic opponent of Westminster, but he, with his sassy ebullience, is a more divisive figure in both nations. Sturgeon is a plainer speaker – less entertaining and less lyrical – but her success as the nationalists’ leader is unprecedented.

No explanation comes quickly to hand. The cause cannot be easily separated from the personality – it is safe to say, for example, that she would be rather less popular if she led the Scottish Tories – but her effect on the non-Scottish audience during the TV debates demonstrated she has gifts that can stretch across political and national boundaries. Empathy and an easy, apparently unrehearsed confidence are two of these gifts. A third is that elusive quality known as authenticity, with its implication that her personality, like ours, has not been bent out of shape by ambition or the needs of politics – that she remains “one of us” in a larger sense than Margaret Thatcher ever imagined the phrase.

These are broad perceptions – the facts are more complicated. As the Scottish journalist Peter Ross has written: “The country’s relationship with her is casual, familiar; we are on easy terms. She is seldom ‘Sturgeon’, usually ‘Nicola’, sometimes ‘Wee Nicola’ ... [but] it is difficult to understand why this has happened.” Ross thought that the “companionable way” people felt about her as someone like themselves was mistaken. Instead, he wrote, she was “an outlier, a prodigy, an alpha female who, from childhood, was set upon political success. As an individual she is remarkable, but it is as a type that we recognise her: the clever girl from the small town; the lass o’ pairts; sensible, dutiful, a grafter.”

Sturgeon will be 45 this summer. She was born in Ayrshire in July 1970, a month after Ted Heath’s Tory party won the general election that was also the first to send an SNP member to Westminster. (The SNP had briefly held two seats won at byelections, in 1945 and 1967.) Her father was an electrician and her mother a dental nurse; they had married young, aged 21 and 17, late the previous year.

“A fairly standard, normal, working-class family” is how Sturgeon has described her background, which means that she grew up in a council house and went to a state school. English politicians, especially but not exclusively those in the Conservative party, sometimes feel the need to present this kind of childhood as evidence of their early aspirational struggle, or proof that they know “the problems of ordinary people”. (Or, in the case of the Labour MP Emily Thornberry, who was sacked from the shadow cabinet after tweeting a picture of a house draped in St George’s flags, that they aren’t snobs.)

But in postwar Scotland, most children of Sturgeon’s generation grew up in council housing. Slum clearance programmes in every Scottish city and town had enormously increased the number of council properties. In the 1960s and 1970s, about 60% of Scotland’s homes were rented by their occupants from local authorities and housing associations, twice the proportion in England; it is said to have been the largest public-to-private ratio of housing stock in any country west of the Soviet bloc. Alex Salmond grew up in one, as did Alasdair Gray, Ian Rankin, Jim Murphy, and this writer as well. The list is long; those on it rarely present their story as one of escape. Compared with what had gone before, they were good places to live.

The Sturgeons’ slice of this Scottish normality was a street in Dreghorn, a village that once stood on the edge of a coalfield; the last pit closed in 1963. By the time of Sturgeon’s childhood, it had become a suburb of Irvine, a port that was then expanding inland as the last of five new towns that were intended to give the Scottish economy a fresh start, as well as improve the lives of those who moved to them. It was here that Sturgeon attended her primary and comprehensive schools and, as a 16-year-old, joined the SNP. Her parents live today in the same house, which, according to Sturgeon’s biographer, David Torrance, they bought under Margaret Thatcher’s right-to-buy scheme in the 1980s.

It is a pleasant-enough place, a typical lowland settlement that is neither densely urban nor truly rural. In the Sturgeons’ street, a series of 1950s terraces backs on to greenery and a river. The village’s main street is much older – one of those long, straight thoroughfares that give so many Scottish villages their simple linearity. In Dreghorn’s case it contains three or four pubs, two barbers’ shops, a Betfred, a dairy, a florist, a mini-market and a post office. To supply any lingering spiritual needs, a handsome 18th-century kirk stands at one end and a nonconformist Ebenezer Hall at the other – both still in use. The old school, a large red-sandstone Jacobean building that opened in 1908, now houses a micro-distillery that makes sake, not whisky. A plaque on the village hall announces Dreghorn as the birthplace of John Boyd Dunlop, inventor of the pneumatic tyre.

The main street has remained relatively undamaged by the recession; despite a bus every seven minutes to Irvine and its mall, few shops seem to have closed. There are six Indian and Chinese takeaways and one fish-and-chip place, which seems a lot for a population of about 4,000 (“People don’t cook,” my taxi driver said). Men stood smoking at the doors of the pubs. Outside the Eglinton Arms, I asked one of these groups where Nicola Sturgeon had lived and a man pointed over the road and said: “That’s where the bus shelter used to be. That’s where she used to hang about wi’ the boys.”

He was teasing: didn’t newspaper reporters like details like these?

“Aye, she’d hang around there and then she’d be away up the munt wi’ wan o’ them,” he said.

I wondered about “the munt” and inside the pub discovered it was Ayrshire dialect for the mount, a freestanding hill at the village’s eastern end surmounted by a stand of trees and a war memorial. A man at the bar said it was a navigational aid in the days of sailing ships and the last piece of the mainland that an outward-bound passenger from Irvine might see.

I walked up the track to the top and looked west. Given the shortness of the climb, the view was unexpected and sensational. To the left, steam rose from the chimneys and complicated pipework of a busy paper mill. To the right lay the village and the northwards curve of the Ayrshire coast. Further off, a freighter moved slowly up the Firth of Clyde, a red hull against the faint greens and blues of the Isle of Arran, the peaks of which were smothered in cloud. Alex Salmond has often talked about how his nationalism had its foundation in listening to his grandfather’s stories of old Linlithgow, a historic town celebrated as the birthplace of James V and Mary Queen of Scots (and Salmond himself). Dreghorn can hardly compete with that romance, but this view, I thought, might have offered Sturgeon something similar: a memorable and distinctive landscape hung as a backdrop to a village that, thanks to John Boyd Dunlop, was home to an entry on the long scroll of Scottish inventions.

In fact, Sturgeon joined the SNP for plainer reasons. While Salmond’s generation had been drawn to the idea of Scottish independence by a combination of the past and the future – in which, to put it crudely, William Wallace strikes a gusher of North Sea oil – Sturgeon was pushed towards it by events in the 1980s. Salmond joined the SNP in 1973 as an 18-year-old student at St Andrews University; the “It’s Scotland’s Oil” campaign that changed the party’s fortunes began the same year, but the nationalist anthems remained focused on the 14th century. Around the time Sturgeon joined in 1987, the factory closures and unemployment of the early Thatcher years gave nationalism a new song. “Bathgate no more, Linwood no more, Methil no more, Irvine no more,” the Proclaimers sang in Letter from America, a record she played constantly (“I drove my mum and dad mad”) because it reflected and reinforced her anger at the social damage she saw around her.

Thatcher was the common enemy. According to Sturgeon, ‘I hated everything she stood for.’

Many of her age group felt the same way, but not always with the same result. The shadow minister Douglas Alexander, born three years earlier than Sturgeon, joined the Labour party as a schoolboy soon after the Linwood car plant, which was close to where he grew up, closed in 1981. For him, the SNP wasn’t an option. “A politics that defines itself by [national] difference holds no appeal for me,” he said when I met him last year. What mattered was “social affinity” – a pan-British idea of solidarity that had created the welfare state. But only a year or two later Sturgeon was reaching a different conclusion. Thatcher was the common enemy: according to Sturgeon she was “the motivation for my entire political career. I hated everything she stood for.” The difference lay in what was to be done. Labour, which at that time opposed Trident, looked to be the natural home for a CND-supporting daughter of a working-class family in the west of Scotland. She chose the SNP instead, she said in a speech in 2012, “because it was obvious to me then – as it still is today – that you cannot guarantee social justice unless you are in control of the delivery”. In other words, as the later mantra of the SNP had it: it’s no use the people of Scotland voting Labour if what they end up with is a Tory government.

Of course, this may be a retrospective gloss; the decision-making processes of 16-year-olds are usually mysterious to their middle-aged selves. But Sturgeon does seem to have been an uncommonly single-minded teenager, instilled by her parents with a belief in the value of hard work that was once – in John Boyd Dunlop’s time, for example – proclaimed throughout the world as the keystone of the Scottish character. “There is nothing in your background that inherently holds you back or means you can’t achieve what others can achieve,” she has said. “You are the master of your own fate, and if you work hard you can do what you want.” Andrew Carnegie or Samuel Smiles might have said those words; Margaret Thatcher or Alan Sugar might have repeated them. But they come as a surprise from the leader of a party that has positioned itself to the left of Labour in what likes to think of itself as a more sharing and caring country than England.

At any rate, she worked hard for the party from the beginning. No present-day party leader understood the significance of doorstep politics as early as she did – the value of canvassing, leafleting, the face-to-face interactions that teach candidates about the people they represent and how to win their votes. And no other party leader was so persistent in the face of such frequent defeat. The SNP began to make its mark in the east of Scotland – farming, fishing and oil territory – in the 1970s, but Labour stood impregnable in the west. In the run-up to the general election of 1987, Sturgeon presented herself at the door of her local SNP candidate with an unsolicited offer of help and was soon pushing leaflets through doors – to no great result, as the candidate came fourth and won an even smaller share of the vote than the SNP’s national average (14%). But the 1980s were a bleak decade for the party. However much Scotland hated Thatcher – perhaps not quite as much as the conventional wisdom suggests – the SNP saw little in the way of dividend. It won two seats in the 1983 election and three in 1987; and though the Tory vote was shrinking, it still managed to be getting on for double the SNP’s share. Whatever else, the party in the 1980s was – unlike Scottish Labour – hardly the obvious choice for a careerist.

But a thinner field made for quicker progress. Aged 17, Sturgeon was appointed to the executive of the party’s youth wing, the Young Scottish Nationalists. A year later and by now a law student at Glasgow University, she made an early appearance in the media (in fact, in this newspaper) as a critic of the poll tax, which she cited as an example of “how the Scottish people have been disenfranchised”. Active in student politics, she helped the Hue and Cry singer and nationalist Pat Kane get elected as university rector. And then, crucially for her personal history, she got to know Alex Salmond during his campaign to win the SNP leadership in 1990, when she played a leading role in the “Youth for Salmond” campaign. “A formidable operator,” was how Kathleen Caskie, then working at the SNP’s headquarters, remembered her last year to the Guardian’s Libby Brooks. “Suddenly there were all these young people wearing Salmond T-shirts – the party was still at 15% [in the polls] and nobody had ever seen that level of organisation for an internal campaign before. That was the stage that her relationship with him cemented.”

Then came a long period of electoral rebuff. In the general election of 1992, aged 21 – the youngest candidate in the UK – she fought the safe Labour seat of Glasgow Shettleston and came a distant second. A month later she failed to win Irvine North in the district council elections, and failed again in 1994 and 1995 when she contested seats on Strathclyde Regional and Glasgow City councils. Her next attempt at Westminster came when she was selected to fight Glasgow Govan in the general election of 1997. The prospects looked bright: SNP candidates had won Govan twice at byelections – Margo MacDonald in 1973 and her husband, Jim Sillars, in 1988 – and Sturgeon did her best to exploit allegations of vote-rigging that followed the selection of her Labour opponent, Mohammad Sarwar. But Sarwar squeezed in to become Britain’s first Muslim MP, and Sturgeon had to console herself with the fact that Govan was the only seat in Scotland where the swing ran towards the SNP, away from Labour.

She was by then working in a civil law firm in Glasgow, but soon after her Govan defeat she moved to a law centre in Drumchapel, one of Glasgow’s biggest housing schemes. There council tenants could find free help to contest eviction notices and stoppages in welfare payments, and unravel the hundred other bureaucratic puzzles that afflict the poor. Inside the SNP, people began to talk of Sturgeon as a future leader, though she had failed to win an election to any public body, even the North Ayrshire council. What finally came to her rescue was the system of proportional representation that the Labour government and its advisors adopted for the new Scottish parliament – a system devised, paradoxically, to install unionist coalitions and keep the SNP at bay. Constituency members of the parliament (MSPs) were to be elected on the first-past-the-post principle, but another category, the so-called “list” MSPs, would be drawn from a list put together by each party, their number in proportion to how many second votes the party had gathered. In 1999, Sturgeon stood again in Govan, this time in the Scottish parliament’s first elections, and again came second to the Labour candidate. This time, however, she was elected via Glasgow’s regional list. The same pattern occurred in 2003. Only at her fourth try, in the Scottish parliamentary elections of 2007, did she win more first votes than her Labour rival to become Govan’s constituency MSP. By the standard of first past the post, it had taken her eight attempts over 15 years to win a majority.

The contrast with the three men we still think of as the main party leaders is telling. Cameron, Miliband and Nick Clegg range from a year to four years older than Sturgeon, yet all became active in politics later than she did. “Struggle” is a word that does not apply to them. They moved seamlessly from Oxbridge into research jobs that gave them easy access to the highest level of political opportunity. None bothered to serve an apprenticeship in the democratic process by standing in unwinnable seats or serving local communities as councillors, and only Cameron (who failed to win Stafford in 1997) has lost a parliamentary contest. Miliband and Clegg won at their first attempts. A tenacious belief in a cause – as well as in her ability to serve it – is the key aspect of Sturgeon’s career; in no other leading British politician’s story – including that of her mentor Alex Salmond – is it so absolutely manifest.

Salmond resigned as the SNP’s leader for the first time in 2000, for reasons that have never been completely clear; perhaps, as he has said, he was simply tired of the job. The party didn’t perform well under his successor, John Swinney, and by 2004 it was looking for a replacement. Sturgeon announced she would stand for the leadership against a small list of candidates that included Swinney’s deputy, Roseanna Cunningham, a longstanding friend who was 19 years older than Sturgeon, and also on the party’s left. Sturgeon had support in the media. The political columnist Iain Macwhirter found that while she “didn’t inspire great warmth”, Sturgeon was “quick on her feet, lacks any ideological baggage and has real determination – unlike ... Roseanna Cunningham”. Salmond, meanwhile, announced: “If nominated, I would decline. If drafted, I will defer and, if elected, I will resign,” which, after Cunningham emerged as the favourite, turned out to be one of the worst-kept promises in recent political history. “Things weren’t developing as I’d hoped,” was how Salmond explained those events to me in an interview six years ago. The result, famous in the annals of the SNP, was a dinner with Sturgeon at the Champany Inn in West Lothian, where he asked her if she would withdraw from the leadership contest and instead run as his deputy.

It was an invitation to be ruthless. A Salmond-Sturgeon ticket would squash any hope Cunningham had of winning – by all accounts, the older woman felt badly betrayed – and meant that Sturgeon would need to ditch her own running-mate as well. But what impressed Salmond and others about Sturgeon at this point was the time she took to decide. “She made him wait 24 hours before giving her response,” the commentator Ruth Wishart remembered. “There is a steeliness in Sturgeon which her petite, stiletto-mounted frame belies.”

Compacts reached at dinners of this kind sometimes have poor consequences – consider Tony Blair and Gordon Brown at Granita – but the Champany Inn deal laid the foundations of a remarkably durable relationship. Sturgeon was Salmond’s deputy for 10 years. “The contrast with the dysfunctional relationship of Blair and Brown is quite startling,” Wishart told me. “Doubtless, there were private eruptions, but at no time has either publicly talked down the other, or, so far as you can tell, privately briefed against the other.” In government after 2007, Sturgeon developed a reputation for efficiency among her civil servants. The common complaint against her was what Macwhirter perceived as a lack of warmth: politics seemed to fill every corner of her life. She started to live with Peter Murrell, the SNP’s chief executive, in 2004 and married him in 2010; they have no children. Even her old parental home in Dreghorn appeared to offer little in the way of conversational relief: inspired by Sturgeon’s example, her mother joined the SNP and became an Ayrshire councillor – an unusual transmission of belief from child to parent.

When I interviewed Sturgeon at her office in Edinburgh in 2013, she seemed determined not to be interesting about herself. It wouldn’t be true to say that I found her “a nippy sweetie” – a Glasgow phrase meaning a sharp-mannered woman, first used to describe Sturgeon by a shipyard shop steward – but she was wary and perhaps slightly chill. “Enamelled” was the word I used. I had read that Tunnock’s – of caramel wafer fame – had baked her wedding cake, which seemed an amusing thing, like having the toasts in Irn-Bru, but when I asked about it she said rather dourly that it had happened only because a Tunnock’s director lived across the street from the couple’s house in Uddingston. I asked about books, plays, the cinema, art galleries, but the most concrete information I got from her was that she liked historical fiction and remembered how as a girl she had enjoyed the books of Nigel Tranter. (Tranter, who died in 2000, was a serious historian of Scottish castles whose novels romanticised the lives of Scottish kings.) She looked impatient at my interest in these things. Whereas Salmond is expansive and informal in his interviews, Sturgeon was restrained and straight.

Facebook Twitter Pinterest It has taken Sturgeon a total of 15 years to win a majority in an election. Photograph: Murdo MacLeod

That interview took place only 20 months ago, but it now seems a different age. The figures have an antediluvian ring to them. That summer the SNP was stuck, as usual, at about 25% in the polls, with Labour leading at 45%. When people were asked about independence, the number of those in favour was usually around 30%. In the 2010 Westminster elections, Labour had won 41 out of 59 Scottish seats, while the Lib Dems won 11 and the SNP six. Scotland’s devolved government was in the hands of the SNP, but otherwise the political map of the country looked much as it had done for the previous 40 years. Nobody then predicted a Labour wipeout in 2015 or an upsurge in SNP support that threatened to deliver a one-party state, or a near-future in which Sturgeon replaced Salmond – though that was always on the cards at some stage – and became Britain’s most-liked political leader.

Last month I went to a public meeting in Inverness to see the new edition of Sturgeon appear onstage. A diet had been followed and a stylist consulted. Though Rory Bremner’s joke about Sturgeon using “Barnett formula” on her hair is hard to forget, she looked polished. She sounded good, too: relaxed, funny and in command. Her cabinet, which leaves Edinburgh sometimes to convene in lesser places, had just had such a meeting, and its members sat on the stage, grouped around the first minister, to take the audience’s questions. Swinney and Cunningham, the once and would-be leaders, were among them. Sometimes you are struck by how different things might have been – not necessarily for the better – if X or Y had become the leader of an organisation or an institution rather than the incumbent. This was one of those times. The audience had come to hear Sturgeon – perhaps just to be in her presence.

She told them she intended “to lead the most open and accessible government that we’ve ever had”; that she was proud to say that, with five women and five men, hers was one of the few gender-balanced cabinets in the developed world. She spoke in a Glasgow twang: “kinna” for “kind of”, “wanna” for “one of”, “ye kin” and not “you can”.

So there we were. A well-disposed audience, some banter from the platform, a good-humoured and enlightened first minister, the promise of tea and biscuits to come. We felt candid and intimate, even though Sturgeon never forgot that some facts can be awkward and are best omitted – never forgot, indeed, to be a politician. Recounting that one of her day’s pleasant duties had been a visit to the railway station to open the offices of the company that has just acquired the London-Scotland sleeper franchise, she mentioned that 20 “high-value” jobs had been created, that the onboard food would be supplied from Dingwall and the mattresses from Aberdeen, while the new staff uniforms had been designed in Glasgow. Every firm got a name check apart from the company the Scottish government had awarded the franchise to: Serco, which has 100,000 staff and tentacles that stretch across the world to wherever it thinks it can skim a profit from an outsourced public service.

After it was over, she spent 30 or 40 minutes posing for selfies. There was quite a crowd. “Let’s get your mum in the photie, too,” she would say, or “Don’t forget the wee boy,” as she rearranged this group and that. At last we were introduced. I shook her hand, and then something strange and unintended happened. My other hand went out and held her forearm – a Bill Clinton kind of movement – as if I wanted to stress my sincerity when I said it was good to meet her. These days she has that effect.

A fortnight later I took an evening plane to Glasgow to hear Sturgeon speak at an anti-Trident rally. It was dark: from the air the settlements of the western lowlands showed up as bright clusters of yellow, white and orange – a surprising density (the lofty question: “What can all the people who live down there do?”) that marked Motherwell, Coatbridge, Clydebank and a hundred other place names that would once have been found on the makers’ plates of locomotives, marine turbines, engine-room telegraphs, heavy-lift cranes, railway bridges and steam windlasses; names printed on cotton reels and impressed on the humble brick. As the source of innovation and well-made things, this is a territory that mattered to the world and helped reshape it. Exploitable seams of coal and ironstone, financial capital, technical skill: in combination, they brightened this night-time landscape for more than a hundred years with foundry fires, blast furnaces and molten iron. Residents liked to brag that you could read a newspaper in the street by the accident of their light.

This was a unionist achievement, centred on a unionist city, Glasgow, which had made its first fortune when it gained access to the tobacco plantations of England’s American colonies. By 1913, Glasgow and its hinterland produced half of Britain’s marine-engine horsepower, a third of its locomotives and rolling stock, a third of its shipping tonnage (equivalent to a fifth of the world total) and a fifth of its steel. No other part of Scotland counted for so much economically or contained as many people – or as many people who lived in such squalid conditions.

Much of this industry had vanished long before Thatcher came to power; as a teenager cycling through Lanarkshire in 1960, I noticed how abandoned pitheads looked as though they had been knocked about by shellfire. But the political habits of the communities that industry created took much longer to die. “Labour Scotland” is how academics Gerry Hassan and Eric Shaw describe this society in their analysis of its decline, naming its three institutional pillars as council housing, trade union membership and local government. For the first two postwar decades or so, in the words of Hassan and Shaw, these things connected Labour to “a feeling of optimism, hope and a shared collective vision of the future”. Each pillar began to crumble in the 1980s. In 1981, council-owned homes formed a majority of the housing stock in 40 of Scotland’s 71 constituencies, largely in the west of Scotland. Ten years later, that was true of only 14 constituencies. Trade union membership fell from 55% of the workforce to less than 40% over the same period. Labour local government had always been paternalistic – and blessings had flown from that – but it was now often inept and sometimes exposed as corrupt. The Catholic hierarchy began its long fall from authority and waned among its flock as a pro-Labour influence.

And yet still the Labour vote held up, like Wile E Coyote before the plunge. Though the SNP won more votes than Labour in the 2007 Scottish parliamentary elections and began to rule as a minority government, it still failed to make significant gains in the west. Only one of Glasgow’s 10 constituencies – Sturgeon’s – had a nationalist MSP. The western breakthrough came at the next Scottish elections in 2011, when the SNP’s share of Glasgow constituencies exemplified the regional trend by rising to five out of nine. The SNP could now think of itself as a truly national party. With nearly twice as many seats as Labour, it was able to form Holyrood’s first majority government and begin negotiations with London to implement the referendum that it had promised in its manifesto. And when that arrived last September, three of the four districts (out of 32 in total) that voted yes to independence turned out to be those places that had once been the great furnace-lit workshop, that had been among the first places on earth to experience the industrial revolution and to support Labour from its very beginnings, and which now contained the poorest, least well-fed, shortest-lived, worst-housed people in Scotland. An outsider’s reasonable expectation was that the strongest vote for independence would come from the areas that had voted SNP for longest – chiefly the prosperous north-east, where Salmond had his Westminster and Holyrood constituencies. Instead – with the exception of Dundee – it came from a population with much less to lose in Glasgow, West Dunbartonshire and North Lanarkshire.

When she was sworn in as an MSP, she swore loyalty 'to the sovereignty of the people of Scotland'

Increasing alienation from a party that had invaded Iraq and indulged the bankers explained some of this; alienation, in fact, from London as the political and financial capital. But as Labour had moved right, the SNP went in the opposite direction, and it was here that Sturgeon had an important influence. As a feminist and unrelenting opponent of Trident, she had in several respects always been more radical than Salmond. Unlike the party leader, she refused to take the oath of allegiance to the Queen when she was sworn in as an MSP, preferring instead to swear loyalty “to the sovereignty of the people of Scotland”. Her opposition to the Iraq invasion was prescient and perfectly expressed: “What a war in Iraq will not do is bring about peace in the Middle East or end the injustices that feed resentment and breed terrorists.” Later, as Salmond’s deputy first minister and health secretary, she was ideally placed to protect free medicine in Scotland and denounce any incursions into the NHS by the private sector in England. Some of her beliefs date back to her teenage years, but her Govan electorate may well have reinforced them: while Salmond’s constituency contained farmers and oil workers and people who were generally doing quite well, very few of these types could be found in the old shipyard lands just south of the Clyde.

The referendum sharpened these attitudes. In the yes campaign, Sturgeon found herself alongside new groups, such as Common Weal, which were more daring in their opposition to neoliberalism than the SNP, and had found an unexpected traction among middle-class public-sector workers, as well as in deprived housing schemes. By this point, however, Sturgeon had developed a view of nationalism that rooted its virtue in social justice rather than national identity. In a speech late in 2012 to a carefully assembled audience of business and civic leaders at Strathclyde University in Glasgow, she quoted the late Sir Neil MacCormick, the son of one of the SNP’s founders and a distinguished academic at Edinburgh University. MacCormick had distinguished between “existentialist” and “utilitarian” varieties of Scottish nationalism, the first demanding independence simply because that is what nations should have, and the second seeing it as a route to a better society.

Sturgeon recognised, she said, that there were some (by implication older) SNP members who were of the first kind, while others were of both kinds, but for her “the fact of nationhood or Scottish identity is not the motive force for independence ... nor do I believe that independence, however desirable, is essential for the preservation of our distinctive Scottish identity. And I don’t agree at all that feeling British – with all of the shared social, family and cultural heritage that makes up such an identity – is in any way inconsistent with a pragmatic, utilitarian support for political independence.”

The debate over the next two years of the referendum campaign, she said, had to focus on “the most effective political and economic unit to achieve the economic growth and the social justice that the Scottish people want. It is, in many ways, our version of the same question being asked across all mature western democracies: how to build a thriving but sustainable economy that benefits the many, not the few. The Westminster system of government has had its chance – and failed. Today, independence is the pragmatic way forward.”

At the time, the SNP billed it as significant speech, and in hindsight it seems even more so. It had disenchanted Labour voters firmly in its sights, though in December 2012 nobody could have guessed how deep their disenchantment would turn out to be or how large was the multitude prepared to defect. Nobody could have imagined their old political representation vanishing as completely as the Ravenscraig steel mill, the North British engine works and the pits of Blantyre. But that is the prospect now.

The most famous event ever to happen in Glasgow’s George Square was the so-called Black Friday rally of 31 January 1919, when many thousands of shipyard and engineering workers assembled to campaign for a shorter working week – 40 hours was the demand – partly to make room for the men who had been discharged from military service at the end of the first world war. Struggles broke out between the crowd and the police and fighting spread through the city. Fearing Bolshevism, the government sent tanks and troops armed with machine guns to guard power stations and other important locations. There was no further fighting, but several trade union activists went to prison and the notion that tanks had suppressed a workers’ insurrection became important to the story of Red Clydeside.

Sturgeon’s audience in the same square earlier this month could never be equated with those long-ago scenes. Perhaps 90,000 people, nearly all of them men, had gathered there in 1919. On 4 April, no more than 4,000 came to protest the presence of Trident nuclear missiles in sea lochs only 20 miles downriver from the city. Many were families. Their placards said “Bairns not bombs” and “Lanarkshire Greens” and on a Saturday lunchtime they were enjoying spring sunshine that had at last turned warm. Several of them came up to say hello to Tommy Sheridan, the former leader of the Scottish Socialist party, and his wife, who both wore narrow and immaculate jeans. They said “Hello pal!” and “Hi darlin’!” and Sheridan bent down to ask a small boy: “Are you the president of the future Scottish republic then?”

Facebook Twitter Pinterest Sturgeon addresses the annual CND Scotland Scrap Trident rally in George Square in Glasgow. Photograph: Jeff J Mitchell/Getty Images

Whoops and cheers and even a lone ululation greeted Sturgeon, who was introduced, in the words of the Daily Mail, as “the most dangerous woman in Britain”. “Do not vote for any candidate that will vote for the renewal of Trident,” she shouted to the crowd. “Is Trident a red line for me? You better believe it. Trident is a red line.”

Then she went down from the stage and into the same huddle of TV reporters that she had left only 10 minutes before. The story that was to become known as Frenchgate had broken overnight: the Telegraph had reported that a memo from a British civil servant claimed Sturgeon had told the French ambassador that she wanted Cameron to win the election. It was hard to see why she would confide in the French ambassador, even if she really did prefer Cameron, and just as hard to see who profited from the story – which was comprehensively denied, and died quickly, though not before Labour figures spread it on Twitter in a losing bid to shore up their Scottish vote.

“The Westminster establishment is clearly panicking,” Sturgeon said to four or five TV interviewers in succession. At one time that kind of statement could have been written off as a combination of hyperbole and paranoia, but now my only reaction was: “And why wouldn’t they be?”

Had the crowd in the square in 1919 threatened the future of the state and its standing in the league table of the great powers? Not really. Had the imprisoned trade union activists who later became radical MPs, the celebrated Red Clydesiders, threatened it? Not really. Had the vast anti-Polaris marches of the 1960s threatened it, with all their acts of civil disobedience and folk-singing optimism? No again. The United Kingdom sailed on.

Only now, with the west of Scotland nearly expunged as an economic force, does the political will of its people keep the rest of the country awake. Here is the queer thing, the thrilling thing and the frightening thing. Among the food banks and the trampled front gardens of the big housing schemes, poor people here have begun to feel they have power.

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