In the spitting rain and a gusting wind, Glasgow University's young nationalists were practising for what may be the most important day of their lives. Activists in the student wing of the Scottish National party, they staged a mock referendum on independence in a bustling precinct in front of the university library.

Mairi Kerr, a 20-year-old Gaelic student from Inverness, was working on the stall, the kitchen table from her flat, handing out ballot papers with the words yes and no in boxes and free SNP ballpoint pens. She parried an attack by one Labour-supporting critic with the cry: "This is not just for the Scottish people, but for everyone who lives in Scotland."

This is the "independence generation" that Alex Salmond spoke of when he unveiled the first legislative programme for his second nationalist government in Edinburgh four weeks ago. Kerr and her colleagues are in the vanguard.

They are the young nationalists who hope to help the first minister put into effect one of the most revolutionary pieces of legislation in the UK's recent history: a bill setting up a referendum on Scottish independence in late 2014 or 2015.

They even had postcards to prove it, with "independence generation" printed in bold capitals on the distinctive canary yellow background which marks out Scottish National party leaflets. The cards invited students to "join the debate today", pointing out Scotland's free higher education and maintenance grants.

The referendum bill was not on Salmond's initial list of new legislation. Secured by the Scottish parliament's first ever absolute majority for a single party, Salmond is biding his time. But that referendum will be staged: it is, as far as legislation can ever be, inevitable.

Students in the nationalist movement speak of a surge of interest on campuses across the country over the past month. Boosted by the SNP's dramatic landslide election victory in May, first year students flocked to nationalist stalls during freshers' week. "We had a good number of people just marching straight up to our stall, saying 'right, where do I sign up?'" said Calum MacLeòid, president of Glasgow University Scottish Nationalist Association, the oldest in Scotland, and a body that predates the foundation of the SNP in 1934.

Scotland's youth will be brought centre stage when the referendum debate truly begins. Salmond's government has mooted extending the vote to 16- and 17-year-olds for the first time. The SNP believes younger Scots are among the most likely to support independence. Polling data shows 18- to 34-year-olds are often the most pro-independence.

Although, troublingly for the SNP and a boost to the pro-UK parties, a majority of 18-24s still back the union, the latest Scotland-wide polls suggest that support for independence has grown since Salmond's landslide. The most recent, by TNS-BMRB, put support for separation at 39% versus 38% against. This is why Salmond is playing his waiting game.

Gail Lythgoe, chair of the Federation of Student Nationalists, said this year's enthusiastic freshers would be campaign leaders when the referendum took place in three years' time. "For us, this is really exciting. By the time the referendum comes up, these first years will be leading the student voice; it's something I'm very conscious of," she said.

Many older voters may still fear independence, said Kerr. But people of her age have lived through 12 years of devolution of Scotland, and feel encouraged to ask for more. MacLeòid agreed. Living with a parliament in Edinburgh has made them hungry for more autonomy.

"Talking about this independence generation is an apt description for us, I think," he said. "We don't remember a time before devolution really. So we've grown up with our own parliament, and the parliament in London saying 'no, you can't do that'. It's pretty hard for us to square that circle."

This is not to say MacLeòid, Kerr and their colleagues got it all their way outside the university library. Alexander Chadwick, a third year biology student, was one of a number of Labour supporters who came up to vote no to independence. "I wanted to balance it," he said. "I wanted to make sure their numbers weren't skewed."

Aidan Flynn, a 19-year-old third year history student, was another. During a ping-ping dispute with the nationalists, he insisted an independent Scotland would increase protectionism and build barriers. As Scotland is one of the most centre-left parts of UK, "we have to make Britain better for everybody. We have a duty to all the socialists in England not to abandon them."

The final result of the mock referendum was 55 for independence to 38 against, a close result given it was an SNP-sponsored stall. But even opposition is a healthy sign, according to Kerr. Despite the intermittent rain, that day's campaigning "seems far more successful than it was when we did this before the election," she says. "At least people are willing to engage with us, whether they agree with us is another matter."

The challenges from Flynn and Chadwick parallel a significant and carefully choreographed step-change in the reaction to Salmond from his opponents in the UK government. David Cameron is intensifying his challenge to Salmond. Several senior sources have confirmed he is anxious to ensure he is not the Conservative prime minister whose greatest legacy was to preside over the break-up of Britain.

At the Tory conference in Manchester last week Cameron accused the first minister of being "a big feartie" (running scared) for refusing to bring forward his referendum, or to set out any details on when and how it would be staged. He said the pro-UK parties had "a very big fight on our hands" to win that referendum, but added: "I'm ready to have that fight."

The so-called "quad" of top cabinet ministers, Cameron, Nick Clegg, the deputy PM, George Osborne, the chancellor, and his deputy, Douglas Alexander, chief secretary to the Treasury, has devised a strategy to counter Salmond's dominance of the political debate in Scotland.

Regardless of the referendum, the UK government's measures to increase Holyrood's financial powers, and Salmond's parallel demands for increased autonomy short of independence, are directly influencing debates about increasing powers for Wales and Northern Ireland. For the first time in centuries, the smaller nations in the UK are winning new freedoms and concessions from London. The UK is changing shape.

The Welsh, reluctant when devolution was introduced in 1999, have now embraced it and want greater financial and political power for the Welsh assembly. Northern Ireland is pressing for greater economic independence, to allow it to compete with the Irish Republic.

Over coming weeks and months, ministers from many major UK departments will be visiting Scotland with increasing frequency for private meetings with business, civic and cultural leaders. Downing Street has hired a new press adviser for Clegg's team, dedicated to Scottish affairs.

"We have to get it across that it is usual for UK ministers to be in Scotland. We have to naturalise that," said one UK government source.

The SNP's landslide victory in May, when it took 68 of Holyrood's 129 seats, shattered the other parties. Labour, the Tories and the Liberal Democrats have had to find new Scottish leaders. Yet even with them in place, Salmond is expected to remain the most dominant and effective politician in Scotland.

Only the Liberal Democrats quickly elected a new leader, Willie Rennie. He is energetic and combative but his party was humiliated at the election, leaving it the smallest of the pro-UK parties at Holyrood. Punished by Scottish voters for its coalition with the Tories at Westminster, it lost 11 seats and was left with just five.

Both Labour and the Conservatives are due to elect new leaders in November, but the Tories are riven by a dispute over proposals by one leadership candidate, Murdo Fraser, its current deputy leader, to scrap the existing party and launch a new centre-right Scottish party.

That battle is heavily influenced by Tory uncertainty over how to combat Salmond and the referendum. Sir Malcolm Rifkind, the influential centrist Tory grandee and former Scottish secretary, believes that if Fraser's plan fails, the collapse in Tory support and influence will make independence inevitable.

Scottish Labour is torturing itself with anxieties about the calibre or suitability of its three candidates – one, Tom Harris, sits at Westminster not Holyrood – while agreeing to give the next Scottish leader much greater power and autonomy from London. Some of its best known and experienced potential leaders lost their seats in May. Senior party figures have vainly tried to persuade Jim Murphy, its sharp and skilled former Scottish secretary, to stand. He will not abandon his career at Westminster.

This vacuum has, in part, forced the UK government to take a much more prominent role in Scottish politics.

Danny Alexander, the most senior Scot in the UK cabinet, says that is appropriate and logical. Scotland has two governments, one in London and the other in Edinburgh, but a decade of neglect by UK ministers since devolution in 1999 has allowed Scots to forget that Westminster and Whitehall still play a significant role in their daily lives, he believes. The UK government spends £26bn a year in Scotland on things such as welfare benefits, defence and scientific research, a figure close to the devolved government's £30bn budget.

Iain Duncan Smith, the work and pensions secretary, David Gauke, a Treasury minister, and Peter Luff, a junior defence minister, have all already visited Scotland this autumn. Now UK ministers are also trying to neutralise Salmond's overseas offensive. Central to his plan to build a much more powerful parallel government in Edinburgh, Salmond has led numerous foreign trade delegations, to Frankfurt, Bilbao, Paris, India and the United States, and is about to take his third trade trip to China, building direct industrial, cultural and political links with Beijing.

Michael Moore, the Scottish secretary and Scotland's voice in the UK cabinet, is aiming to trump that. He has set up a "trade and growth" board for Scotland and will soon lead Scotland's "largest ever trade delegation to Brazil", a visit which will take place on St Andrew's Day, the patron saints day beloved by the nationalists.

The last Labour government and the present coalition had been "too standoffish as it applies to Scotland", Alexander said. "We have to assert our role much more as a government of Scotland for the people of Scotland than has historically been the case since devolution. When devolution happened a lot of UK institutions thought 'Scotland is devolved now so we don't need to engage so much.'"

Sitting in a bustling cafe near the Scottish parliament, Alexander is more combative still about Salmond. Like many of the first minister's critics, he says he is astonished by Salmond's delaying tactics over the Scotland bill, the major piece of new Westminster legislation which will hand Holyrood control of income tax rates, give Scotland the power to borrow £2.2bn and control minor taxes such as stamp duty and the aggregates levy.

Alexander said these provisions "are hugely ambitious, hugely significant actually and in some ways more significant than devolution itself. This is the biggest shift in financial powers and accountability within the UK for 300 years."

It is also the most significant area of conflict between London and Edinburgh. Countless opinion polls suggest Scottish voters want greater devolution rather than independence, by a margin of roughly two to one.

Mindful of this and empowered by the May election result, the SNP government is demanding the UK government increases Scotland's economic powers still further.

Among Salmond's six demands are control over corporation tax and excise duty, much higher borrowing powers, and authority over the crown estate, which controls the UK's seabed.

Salmond insists he is doing what he was elected to do: championing Scotland's interests by pushing for more power. Alexander accuses Salmond of more "grudge and grievance" politics, and insists he is jumping the gun. The current Scotland bill provisions already involve very complex tax arrangements and adjusting the block grant Scotland gets each year from the Treasury; it would be far better to get those in place and working before demanding even more ambitious powers.

"One thing I find incredibly frustrating in this whole process is for the Scottish government, which claims to want more responsibility for Scotland, the SNP are still not clear whether they really support the Scotland bill or not," he said.

"The Scottish government seems to be spending a vast amount of effort and time campaigning for additional things and not a great deal of effort or time working out how the existing provisions are implemented."

But at the heart of this dispute is an area where there is common ground: the notion that Scotland may yet get even more power. Alexander agrees that devolution will continue: Moore has mooted air passenger duty being devolved and Alexander has just announced that the Treasury will allow the Scottish government to issue its own bonds to raise money.

The dispute is over how fast and how significantly devolution evolves. Alexander wants to approach this slowly. "Let's get this thing working, see how they work, identify problems, identify new areas where we might want to take further steps on but do it slowly and deliberately and not in a great rush driven by politics," Alexander said.

In parallel with the UK government's new strategy to combat Salmond, a pro-union movement is emerging, if hesitantly.

Barely half a mile from where Kerr and MacLeòid hosted their mock referendum, Glasgow's only Tory councillor, David Meikle, was nursing a new anti-independence pressure group – the only one so far in operation – which had been set up a few days before, called One Dynamic Nation.

Meikle believes he too represents Scotland's youth: he was the Tories' youngest councillor in Scotland when he was elected to the city council in 2007 at the age of 22, and remains so.

One Dynamic Nation (ODN) is being funded by two businessmen, Barry O'Neill, a Labour supporter working in the energy sector, and Anthony Pfaff, an actuary and business consultant whose IT company built the campaign's fresh-looking website. It has a desk in the company's office in the city's West End.

It has been a slow start for Meikle. Launched without great fanfare on 29 September and no marketing, the website has had nearly 2,800 hits in its first five days, a trickle of donations, but a more modest 21 signatures to its "stay in the UK" petition and just 10 people signing up to join and five to volunteer. A Lib Dem activist in London wants to set up a branch in the capital. The Tory students' association at Aberdeen University wants to join.

Business donors and political figures have been privately supportive but tentative about endorsing or funding ODN; they want it to prove itself first, Meikle said. He hopes they can slowly build up a genuine grassroots, non-party political movement that may eventually become the figurehead for the pro-UK campaign in the independence referendum.

It was set up three years before the referendum because its backers felt a sense of urgency after Salmond's landslide left the pro-UK parties in disarray and the SNP in control of Scotland's political landscape, Meikle said. "There was a vote of no confidence in these parties. We had to try to fill the gap, to promote the union. That result was like a wake-up call," he said.

It is partly modelled on the online campaigns forum 38 Degrees, which has co-ordinated civic political action against phone hacking, the forestry sell-off in England and Donald Trump's push to evict residents around his golf course in Aberdeenshire.

ODN's title is deliberately ambiguous; the "nation" could be the UK or Scotland. Nationalists have accused the campaign of denying Scotland's nationhood. "We feel the UK is one dynamic nation," Meikle said. "Obviously, we're proud Scots but we're also proud of the UK, to be British. In Scotland, there's a strong issue with identity and nationhood, but we also feel there's a strong British identity, in terms of all the parts of the UK."

Meikle is a lonely campaigner. The pro-UK movement has yet to gather momentum or significant support. Pro-union party leaders insist they are biding their time but in private admit something crucial: they still have no coherent or agreed campaign to combat Salmond's methodical drive to independence.