Nick Clegg remembers two questions cropping up over and over again in the weeks running up to last year's general election campaign. "How come so few members of the public know who you are?" and "Why is Vince Cable not the Lib Dem leader?" were the journalists' favourites. Clegg's obscurity was the story in those distant days and it irritated him intensely.

Exactly a year ago on this Friday, all that changed. "Cleggmania" was born. Clegg went from the status of political also-ran to national hero overnight. In the first television debate of the election campaign on 15 April, he oozed confidence, delivering promises of change. "I believe the way things are is not the way things have to be," he announced in front of 9.4 million viewers, adding: "Don't let anyone tell you the only choice is the same old parties. We can do something new, something different."

With one hand planted in his pocket – so as to appear relaxed – he addressed each questioner by name; Jacqueline, Joel, John, Robert, all of them were name checked. Smooth, young and fluent alongside a surprisingly tense David Cameron and a stilted Gordon Brown, everything came together. Clegg, who had remained pretty anonymous until then despite his best efforts, seemed appealing, different and new, as he seized his moment.

The instant audience polls declared him the runaway winner. The newspapers agreed. "He used the limelight of the historic broadcast to devastating effect," said the Times. By the weekend, the Lib Dems were riding the crest of a powerful wave of popularity as they pushed ahead of Labour and the Tories in the opinion polls. Clegg, it was said during those unreal days, was almost as popular as Churchill in his pomp.

When they reflect on an extraordinary year of fluctuating fortunes, those close to Clegg admit they cannot bear to look back at film of that TV debate and all the hostages to fortune it threw up. They recall that period not as the most exciting of the last 12 months, but as the most disorientating and, in some ways, the most testing. Clegg found it the same. "We went from obscurity to all that overhyped feeling in days. We were a small team and we weren't used to it," recalls a member of his inner circle. On a train journey to Wales the weekend after the debate, Clegg was mobbed. Student voters were flooding Twitter with messages of mass support. He and his team were struck by the physical proximity of the press and the admiring public. It was all so sudden and so intense.

Nick Clegg's political life was just beginning to assume an extraordinary, erratic rhythm of high and lows, of achievement and disaster, that would endure for the whole year, testing him and his supporters to the limits, psychologically, personally and professionally.

Cleggmania was to prove short-lived. The election on 5 May saw the Lib Dems lose five seats as the earlier, wild predictions that they might seize more than 100 came to nothing. Clegg was "deeply disappointed" as he watched his party lose out on seat after seat – particularly a batch in the north of England that he believed were in target range – by small majorities, as the Lib Dems were caught in a classic Tory/Labour squeeze. "It was depressing," said a colleague who was with him on the night. "We thought if we couldn't do it then, with all the advantages we had, then when would we?"

But no sooner had Clegg's fortunes dipped from the heights than extraordinary opportunity offered itself once more. Just over a week later, in the Rose Garden of No 10, a beaming Clegg would stand alongside Cameron, as deputy prime minister, having formed the first coalition government since the second world war.

It was such a happy event that sketch writers likened it to a civil partnership. In the coalition agreement were commitments, crucial to the Lib Dems, to a referendum on electoral reform, tax reform and more money for poorer pupils in schools. It looked a decent deal for them.

Since that sunny day in Downing Street when the flowers were in bloom, no one, and certainly not Clegg himself, would pretend it has been easy. In fact quite the reverse.

The hero of the first TV debate has become the hate figure of students and the object of ridicule of cartoonists, who depict him day in day out as "Clegg minor", Cameron's public school fag, always doing his master's bidding.

The man who once got so frustrated at being ignored by the media has become its punch bag – and the frustration is now at what he often sees as the futility of the press. His popularity and that of his party has nosedived as he has been taken to task for breaking election promises on everything from student tuition fees to VAT and spending cuts. An election broadcast in which Clegg talks of the broken promises of the "old parties" is too much for Lib Dems even to think about these days.

Last week was yet another testing one for Clegg in which a crackdown on unpaid internships backfired when it was established that his party awarded them and that Clegg himself had been a beneficiary. He gave an interview to the New Statesman in which he said, in passing, that he often cried when listening to music. He felt he was just being honest and showing his emotional side. But his aides were furious at the way the story was promoted and carried in other papers. "It was if he cries all the time," said one. "Unbelievable!" Lib Dem MPs could not believe that Clegg could have been so naive.

Clegg, in the eyes of some, can do no right. "Everyone seems to want to say that Nick is miserable, that he is down all the time. But it is not the case," said a friend and colleague. "He just says things like that, that other politicians wouldn't, because he is more normal than most. He actually answers questions rather than thinking, 'Oh no, I might he caught out'."

Fellow Lib Dems say the sniping and cheap headlines test Clegg's patience and that he occasionally wonders if it is all worth it. He also gets frustrated by those who fail to understand that life in a coalition is complex and difficult and that it depends on compromises that may not rest easy with any single party's agenda, but that are necessary to govern.

They insist that if anyone can survive what the media throws at him, it is Clegg. "He has a lovely wife and three boys he adores and politics is not everything to him. He has not been in Westminster long. He keeps things remarkably in perspective given what he has to take, just because he has so much else in his life."

Very early on in Clegg's extraordinary year, when Cleggmania was in its infancy, Paddy Ashdown, the former party leader, had seen danger signs. Backstage after the first TV debate he knew that Clegg and the Lib Dems had disturbed the old order, the old way of doing things. They were going to make a difference to the way the country was governed. "Paddy was clear as we gathered afterwards in the room behind the stage that the rightwing press (which hated the idea of coalition government) would unleash everything at us after the first debate. He told us to prepare for it, to be ready."

Ashdown was proved right. On Thursday 22 April, a week after the first TV debate, four Tory-leaning papers went for Clegg on their front pages. The headline that shocked the Lib Dem leader most was one in the Daily Mail that took an article he had written eight years before about attitudes to the second world war to compile a story headed "Clegg in Nazi slur on Britain".

Clegg is said to have been furious with both the Mail and Cameron, who refused to condemn the story, though not that surprised by the reaction of the Tory leader whom he repeatedly labelled at that time as a "fake". "I must be the first politician to have gone from being Churchill to a Nazi in less than a week," he said.

As he shot to fame and popularity during the TV debates, Clegg was, however, sowing other seeds of his future difficulties in ways that even wise heads in the party did not see as that problematic at the time.

To court popularity, he promoted himself as the agent of a new, honest politics, a different kind of country even, in which leaders would deliver on promises – and not just drop them when power required them to do so. One party political broadcast opened with scenes of litter blowing in the Westminster wind – the broken promises of the "old parties".

In his concluding statement to the third and final TV debate, Clegg posed, somewhat piously, as a different type of leader who would stick to his word. "Just think how many times you've been given lots of promises from these old parties, and when they get back into government, you find that nothing really changes at all. We can do so much better than that this time."

They were decent enough lines for the leader of a third party with no chance of winning power. But with a hung parliament a genuine possibility, it was a massive hostage to fortune that he would come to regret. In the run-up to election day, Clegg had made his own promises on policy that people would expect him to keep if he ever got his hands on the levers of government. He had signed a pledge to oppose any rise in student tuition fees. He had posed in front of a poster that warned of a Tory VAT "bombshell" – making clear he opposed such a move. And he had been clear that he wanted to cut spending more gradually and less deeply than the Tories.

Once in coalition, he broke those pledges too readily in the eyes of a large section of the electorate. First came his backing for rapid and deep spending cuts, then his endorsement of George Osborne's hike in VAT from 17.5% to 20% in last June's emergency budget. But the most explosive breach of electoral trust was his backing for government plans to treble tuition fees. When students – the very constituency Clegg had gone out of his way to court – marched through Westminster and then stormed Tory HQ in protest, he was genuinely shaken. Now he admits he should never have signed the pledge not to raise them. One MP friend says he is desperate to win back the respect of students. "He took the protests very seriously. He thought the violence was terrible but he saw it was a serious protest." To some extent he felt a measure of personal responsibility.

Clegg also accepts now – indeed he did as much in an interview with the Observer last autumn – that the Lib Dems will have to conduct election campaigns differently, and more carefully, in future. With coalitions as likely as not from now on – and with the Lib Dems the potential kingmakers – the easy throwing out of promises that might have to be watered down or compromised will not be repeated. A core set of principles will be established, and key demands laid down, but pious promises to deliver on everything will be avoided.

This weekend Clegg is again battling his own party over the extent of health reforms. Lib Dem activists oppose most of Andrew Lansley's proposed changes and want Clegg to exercise his influence by watering them down. Clegg is caught once more between the demands of his own party and those of the Tories in the coalition. The pressure never relents.

At Easter the Clegg family is heading for Norfolk for a family break. His press team say both he and Cameron resist taking a decent long holiday because they are so dutiful. The reality is they are afraid of what would be said if they did. When Clegg recently headed for a skiing break in Switzerland, with his family, he was called back early for emergency talks on events in north Africa. Friends say he would love, and needs, a good holiday more than anything. "He always looks tired and exhausted even when he is not," one said. He adores and looks forward to Saturday mornings watching his three boys playing football in south London and the odd weekend at Chevening, the grace and favour residence he shares with William Hague.

All attention for Clegg and the Lib Dems is now turning to "super Thursday" on 5 May, the day of local elections and the referendum on a switch to the alternative vote. Clegg knows that his party is likely to be hammered in the elections because they are down in the polls and are unpopular, but will hold out hope that the public might still back AV, delivering a central Lib Dem objective. But even if they do not, he is in reasonably optimistic spirits.

He and his aides can reel off the achievements of the Lib Dems in government without thinking. They list the pupil premium for children from poorer families, income tax breaks for those on low incomes, the scrapping of identity cards, progress on civil liberties, the referendum on electoral reform and more. Recently a group of aides met to think up lines for the next TV election debate. "It was based on the idea that if we can deliver that lot with 57 seats in the Commons, imagine what we can deliver with 87."

One MP colleague said: "If Nick can survive what he has survived so far, then he has got what it takes to go the course. In fact I think the good British public will see, over time, that he is a basically a good guy in a hell of a difficult position who is doing a decent job for the country."

If that happens the cycle will be complete.

A YEAR AFTER CLEGGMANIA, WHAT THEY THINK NOW

ALASTAIR STEWART

ITV News presenter and moderator of the first party leaders' television debate

Nick Clegg's aide, Danny Alexander, towered over me in Granada's reception and told me all was well with his man. Rules understood; no need for a pre-Debate chat; all well.

The home of Coronation Street was abuzz – from studio to green-room to smoking area in the car park, there was a palpable sense of excitement ahead of the first ever leader's debate.

I didn't see Nick, or the other two, until three minutes to on-air when they joined me, backstage. There was much patting of hair, lots of cufflink fiddling, and nervous smiles to the audience when eye contact was made. But they were all focused.

Nick went first with his opening statement. I knew, within minutes, this was an outsider on top of his game. The relative amateur eyeballed the camera; he smiled; he stressed he wasn't "them"; and he said we couldn't go on with the old ways. His pitch was that he was "an honest straight guy, above the fray"

Honest? Straight? That's for you to judge. Above the fray? No way. He was calmly possessed with his purpose. David Cameron looked frit; Gordon Brown in self-confident denial.

I felt it was "game, set and match" to Clegg very early on. As the 90 minutes charged by, he did little to change my view. The others stumbled from "I agree with Nick" to caustic barbs which only made it worse for them. My view was confirmed in the spin-room. The next morning, hungover with emotion and a sense of having been a part of something rather special, I returned to preparing for my role as anchorman of our results programme on the night of 5/6 May .

On that night, the Lib Dems successfully and unexpectedly defended Torbay, Bath, Chippenham and Lewes but still managed to end the fray with four fewer seats than they went to war with.

The Lib Dems' share of the vote rose 50% the morning after the debate but had only risen by 4% come polling day. From leaders saying "I agree with Nick" to not enough voters agreeing with Nick.

It was an amazing event but may have left Clegg wondering "what was that all about?" and, now, "why did I bother".

TIM MONTGOMERIE

Editor of the ConservativeHome website

In the list of most stupid political decisions, the Tories' agreement to TV debates should rank near the top. When you are ahead in the polls you don't agree to a potential game changer. Unfortunately, anxious to please Rupert Murdoch's Sky News and with an exaggerated confidence in David Cameron's message, the Tories gambled. At that first debate Nick Clegg channelled the anti-politics mood of the post expenses scandal era. On the sidelines, I watched the colour drain from Tory spin-doctors' faces.

The Clegg bubble did enough to disrupt the Tory campaign and produce a hung parliament. But the man who promised a new politics was guilty of the worst kind of politics when he broke his promise on tuition fees. I doubt he'll ever recover.

JACQUELINE SALMON

An optician from Burnley, Lancashire, who pressed the party leaders on crime during the first TV debate

I went along to the first debate because I wanted to speak to all the politicians about the problem of crime in northern towns. I was impressed with Nick Clegg's answer – I think he connected far better with the audience. He used names quite a lot which the other two didn't. I didn't know much about him before that night, but I was impressed and I definitely got caught up in "Cleggmania". I thought his whole campaign was very successful; he made everybody listen to him – maybe the first time for the Lib Dems.

I was made up with the Lib Dem/Tory coalition; I'm glad he didn't go with Gordon Brown.

He's between a rock and a hard place; I don't see how he could have done things much differently. He's compromised his political goals, unfortunately, but I don't see that he had a choice.

CHRIS RIDDELL

Political cartoonist of the Observer

Poor old Nick Clegg, the political cartoonist's friend.

A year ago I drew him for the first time as a bright young contender in the leadership debate boxing match, his heavyweight opponents battered and bruised by comparison.

Then came the coalition and little Nick became the central character in his own political fairytale, tripping off into the woods as "Little Clegg Riding Hood" with his basket of electoral reform clutched closely to his yellow cape while the rightwing Tory Wolf lay in wait.

The fairytale didn't last, but I found no shortage of Clegg metaphors to chart his hapless progress. He was the RCA dog listening to his master's voice, a cracked record repeating "We're all in this together" over and over. When Cameron and his wife had a baby, Clegg was "Nanny Mcpheeble" struggling with coalition disposable nappies, and when Cameron returned from his globetrotting adventures faithful old Nick was the Downing Street Doormat for Dave to wipe his feet on.

And then came the great student fees betrayal, and Nick Clegg really had gone all the way in his relationship with the Tories. I drew him puffing on a post-coital cigarette, full of self-loathing, as his partner promises him a Tory peerage.

That is the thing about Nick. He has been prepared to do what it takes to be in government and he wants to be taken seriously. But his bland good looks, the boyish hair and twinkling eyes conspire against him. He is the coalition clown, part lightning rod, part punchbag, but always ridiculous. It is the historical fate of vice-presidents in America visited now on our "vice prime minister".

Poor old Nick Clegg, everybody hates him and he really, really cares.

OLLY GRENDER

Lib Dems' former director of communications

Liberal Democrat leaders are a blank sheet of paper until their first general election. So when the nation tuned in to the first leaders' debate they were amazed to discover there was something else on offer, Nick Clegg. I was jealous that night of the others in the spin room, having already committed to being in a TV studio.

His stock rose to an unsustainable level. He went from comparisons with Churchill to Hitler in one week. It was a strange moment of X Factor mania meets regular politics. The tabloid attacks were inevitable.

At HQ, those for whom this was a first election were swept up by the possibilities. Those who had lived through the SDP bubble and other false dawns were quietly sceptical.

ANTHONY KING

Professor of British government at Essex University

Like most manias, Cleggmania was always a delusion: a decent and modestly competent second-order politician thrust by the media into the role of hero-statesman. To be sure, the opinion polls reported that in the first TV debate he performed well in viewers' eyes; but only one voter in four watched and undoubtedly a disproportionate number of them were already Lib Dem supporters. Essentially a non-event, the debate was trumpeted as a major one.

Then, after the election, David Cameron, to everyone's surprise, offered Clegg and his followers posts in a coalition government. With the financial markets in turmoil, it was an offer that Clegg could not refuse. As deputy prime minister and David Cameron's new soulmate, he was made to look even more heroic and statesmanlike.

Now he is cast in the role of villain. But he was never a hero and does not now deserve to be deemed a villain. Clegg and the Lib Dems are stuck. They cannot bring down the government, lest they cause turmoil in the financial markets and lose most of their seats.

Their power in the coalition is negligible. They cannot insist on anything. Their only weapon is persuasion. Last week's backtracking on Andrew Lansley's NHS reforms suggests that, after all,they can be quite persuasive.