A political tug-of-love as rivals woo the man who could be kingmaker

Largely unknown on the national scene, he had quit as an MEP the year before to concentrate on securing a seat at Westminster in the leafy constituency of Sheffield Hallam, held by the Liberal Democrats since 1997.

Fast forward to today, and he is still in campaign mode but, after a meteoric rise, it is as leader of the party – and potentially, if opinion polls pointing to a hung parliament come true, the most powerful leader since the party was formed.

Soon Mr Clegg will square up to Gordon Brown and David Cameron in the first televised debates between party leaders during an election campaign. But for all the animosity in the exchanges that will ensue between them, Mr Clegg is hot property because of the role he may fulfil if the two main parties fail to win an overall majority.

Last year, the Tory leader said there was "a lot less disagreement than there used to be" between the two parties while last month the Prime Minister added that the Liberals were "closer to us on tax and public services".

The real question is if the Lib Dems do hold the balance of power, what would they do? Prop up Labour or support the Tories? The party's natural instinct would surely lean towards the left, but – having shifted policies towards public spending cuts – Mr Clegg himself is often seen as a Tory in disguise.

Having initially refused to engage on the question, Mr Clegg has

softened his response to say that the party with the "strongest mandate" – whether that means votes or seats is unclear – has the "moral right" to seek to govern.

"It's not whether David Cameron, or Gordon Brown or Nick Clegg are kingmakers," he says. "There are 23 million kingmakers. We the politicians do what you, the voters, tell us."

Adamant there will be no deals between the parties, he insists his party is "not for sale" – but he is prepared to set out his agenda if either the Tories or Labour comes calling for his support.

"I can tell you the principles on which we will vote," he says. "Those principles will be to deliver fairer taxes, smaller class sizes, more one-to-one tuition for children, a new green, fair economy, a new politics.

"That's what I'll fight for whether we find ourselves in hung

parliament territory or not, whether we're governing on our own or in opposition.

"I think that's a pretty clear guarantee I can give to people. If you vote for the Liberal Democrats that is what you will get in whatever circumstance the future throws up."

If he was not leading the party, Mr Clegg might find himself with more of a challenge for his own seat, given it used to be the sort of true blue constituency that Mr Cameron would be banking on winning. A

notional majority of just over 7,000 once boundary changes are taken into account would justify it being considered a marginal, yet

privately the Tories admit his profile – which has helped the constituency raise a staggering 41,740 in donations since the start of 2008 – means they will not dislodge him.

The reality of a gruelling campaign for the General Election, expected on May 6, means Mr Clegg will have little time to spend in Sheffield. Instead, his focus will be on making progress towards his pledge to double the number of Lib Dem MPs – at present there are 63 – within two parliaments. It would give them a number of seats not achieved since the Liberals won 158 in 1923, but Mr Clegg refuses to be daunted.

"I really do think it's only now dawning on many people here in the Westminster village how out in the country at large all bets are off for this next election. It's really wide open," he says, conscious of the impact of the expenses scandal and the economic crisis on public opinion.

"I think there are millions of people who supported Labour in 1997 but no longer want to support Labour but are wholly unpersuaded that the plastic charms of David Cameron will deliver the change they want."

At 43 – 15 years younger than the Prime Minister – Mr Clegg is taking advice from his predecessors in the run-up to the campaign, in

particular Lord Paddy Ashdown, to whom he is close.

"I think he's very supportive of what I've sought to do – which is to be as clear as early as possible," he says.

"Don't try to spring surprises on people in the middle of a General Election campaign. Be clear about what you stand for, what your principles are, then spend a long time explaining it, rather than playing this game of cat and mouse with voters which is what I think David Cameron and Gordon Brown do."

The advice is welcome, as it hasn't all been plain sailing since becoming leader in December 2007. As well as having to steer the party away from a tax-and-spend philosophy as the economic crisis struck, he

faced the resignation of frontbenchers who rejected his orders on how to vote over a referendum on the EU Treaty and there was embarrassment at last autumn's conference as the party's new "mansion tax" proposals unravelled and he faced a backlash over watering down of pledges to abolish student tuition fees.

But over the past year he has matured as a leader, notably inspiring the defeat of the Government over the issue of allowing former Gurkhas

to stay in this country and winning credit on the economic front,

thanks to having Vince Cable as treasury spokesman.

Critics who felt there was too much Mr Angry in the early days of his reign sense a toning down of the hyperbole, which has helped in establishing his authority. Not that he has given it up altogether – ask him about the Government's proposed referendum on whether to ditch the first-past-the-post voting system in favour of the alternative vote, where candidates are ranked in order of preference, and he says it's time to try democracy "for a change".

"What Gordon Brown is producing is a mouse when what we need is much more radical change," he says.

"Sometimes when I listen to Gordon Brown I want to think to myself what planet is this guy on? He's been in charge for 13 years. Why should we believe him now if he hasn't done it for more than a decade?"

Electoral reform has always been a key issue for the Lib Dems – they recently published their own proposals for a proportional voting system which would see the number of MPs in Yorkshire cut from 55 to 44 – and a pledge of clean, open politics is one of four key principles the Lib Dems will campaign on.

Fair taxes, a fair start for all children at school and a rebalanced, green economy are the others.

"I don't believe it's right for politicians – and that's what David Cameron and Gordon Brown are doing – to charge around the place

spraying implausible promises to people on this, that and the other on every day of the week which everyone knows are never going to be

delivered, and not being clear about where their heart lies, what their convictions are," he says.

"Some people may disagree with it, but I've been very open. My

conviction is driven entirely by the desire to see greater fairness in Britain."

With a busy calendar of events in the diary, he is already in "semi-campaign mode" and insists he loves getting on the road, holding town hall meetings and speaking to ordinary people outside the Westminster bubble – something to which, he says, people are responding well.

Soon he will have the chance to address the nation in the first

televised debates between the party leaders. Logic suggests that he has most to gain, being the least well-known of the three, suddenly

presented with a prime-time televised slot. He welcomes the debates as a chance for voters to judge the character of the three men but denies he will automatically benefit most.

"We're all going to have our challenges. You could argue Gordon Brown will be the winner because expectations are hardly high about the way he's going to perform," he says.

"I don't honestly think it necessarily plays better for any one of us – that will be determined on the night. But I do think that people will be the winners by actually having greater information to base their judgments on how they're going to vote."

It is a long way to have come in five years. The next three months will determine whether his stock is still rising.