Chris Huhne is in a hurry. The new Secretary of State at the Department of Energy and Climate Change (DECC) has a vote in the House of Commons and he is still sitting in his office in Whitehall.
The man in charge of delivering on David Cameron's pledge to make the Conservative-Liberal Coalition the "greenest government ever" takes the high-speed lift to the ground floor. But he doesn't rush to his personal bicycle stand – "the security guard assures me I can leave it unlocked and there'll be no problem" – and instead gets straight into a car for the 0.4 mile trip down Whitehall to Parliament. At least it's a Toyota Prius.
In the DECC foyer, a flat-screen television runs, on a loop, footage of the Prime Minister's speech to staff last month, alongside his smiling new Liberal Democrat Energy Secretary, during the earliest days of the new Government. Upstairs, Huhne is still manfully maintaining the charge.
"This was one of the first departments that [Mr Cameron] visited," Huhne said. "He took no time at all to announce that we were going to reduce carbon emissions across the government estate by 10 per cent in 12 months.
"We've got our first meeting of shell-shocked Whitehall officials [this week]. I walked past the Ministry of Defence the other night and all the lights were blaring, the televisions were on, but there was nobody inside. I've already upbraided the defence ministers – if they want to put more money into the frontline troops then they've got to damn well save on their energy bills."
While several Lib Dem party members, even his cabinet colleagues, have agonised about entering a coalition with the Conservatives, Huhne has clearly grasped the opportunity with both hands. In fact, he reveals, barely a month ago he was a lone voice within his party on the vexed question of whether they should enter government at all.
"The negotiating team," he says, "had a number of preparatory meetings before the election campaign at which we discussed scenarios and looked at what might happen."
"If we had to do a deal with the Conservatives if that was the only way the arithmetic worked out, it was likely to be a supply and confidence arrangement [supporting them on key votes] ... because most people didn't think the Conservatives would offer enough on electoral reform in particular to make us be able to do a firm deal."
He confesses he might be "talking out of turn" about the secret dealings of the high-powered team of Nick Clegg trusties that delivered the Lib Dems into government. But it doesn't stop him. "The truth is that we've ended up doing what I was in a minority arguing we should do before the election."
It was an excruciating decision for many Lib Dems – and unacceptable to some of them – but for Huhne it was a natural step. He is comfortable using the language of "new politics" and happily condemns the "old" parties. But, when he speaks about the events that brought about the Con-Lib coalition last month, he sounds like the hard-headed financial journalist, the successful economist, the wealthy businessman he once was.
Huhne said: "If you look at the negotiating team, I was in a minority of one, saying we had to have a coalition come hell or high water, because of the economic problems, and if that meant having a coalition with the Conservative Party, then we had to do that too. We'd just have to bite the bullet.
"I spent five years in the City heading up a team which eyeballed finance ministers and central bank governors at a time when they were facing massive problems. I never want a British Chancellor or a Governor of the Bank of England to be in the same position as these guys were in, and therefore it's absolutely essential that we tackle this deficit."
Huhne did not expect to end up in Government with the Tories, but when they came up with "a good offer", he joined a knot of right-leaning Orange Book Lib Dems, including Mr Clegg and David Laws, who were improbably installed in government a month ago.
When the jobs were being shared out, the man who had set so much store by the need to attack the deficit ("he bored the hell out of us," as one colleague recalled) insisted that the Lib Dems were granted a senior position at the Treasury. But, surprisingly, he did not want it himself – opting instead for what he described as his "dream job" at DECC.
This is a man who was "turned on" – yes, turned on – to the green agenda during a visit to Tanzania with The Economist more than 30 years ago. Ten years later, in a book of his published articles, he declared that it "was going to be the dominant issue in our time, in terms of the potential threat to our existence".
"I can genuinely say that I've been committed on the green and climate change agenda for a long time," he explained. "I've always thought what we desperately need to do is combine the commitment which so many people who are concerned about the green agenda have with some hard-nosed economic analysis to deliver it in the cheapest way so that people can go on enjoying the things they like. Often the green agenda is put in such a way that you have to be hair-shirt; you can't enjoy yourself. This is just wrong."
At the age of 55, after journalism, bossing several City firms, a stint as a Euro MP and twice-failed party leadership bids, he has finally arrived. He is keen to make it plain that he has not been overwhelmed by the promotion: for example, he points out, his office is less grand than the palatial HQ of The Economist in Brussels, overlooking the royal parks, which he occupied 30 years ago.
By necessity, the Secretary of State's brief is more about saving money than spending it, for example, by reducing energy use. "This is not just a carbon-reduction issue: we're spending more heating our homes in this country than they do in Sweden. We might as well be standing outside our houses burning £50 notes. It makes us more dependent on imported oil and gas."
But there will be more contentious issues ahead, not least the question of nuclear energy, which threatens to cause early friction within the Coalition. Huhne insists that he has never been "an ideological ayatollah" on the subject, but he is no friend of the industry and he has already confirmed that there will be no government subsidy for it.
"If people want to invest in it then there will be new nuclear power stations [but] no public subsidy: on that we're agreed," he said. "That's a highly credible commitment given the state of the public finances." And, while he looks forward to a "green tax shift" in future budgets, he accepts that his chances of tackling global warming are threatened by the naysayers with whom he now shares the government benches.
"There are climate-change sceptics on the Conservative benches and I am aware that I have to work hard to keep them on board," he said. "The key point is that they are also receptive to the arguments about energy security."
Moreover, as a former MEP, Huhne is also alive to the potential for rifts within the coalition over Europe. While he argues that the post-Lisbon period presents little immediate danger, the Tories' continuing alliance with what his leader called "nutters, anti-Semites, and homophobes" in the European Parliament – rather than the mainstream European People's Party – could cause problems in the future.
"It's entirely up to them," he said of the Tories' choice of bedfellows. "I'm very willing to give them unsolicited advice [and] I would urge them to rejoin the EPP. But it's entirely their matter and I'm not going to stick my nose into it."
Huhne hopes government will finally dispel the image of Lib Dems as "tofu-eating, sandal-wearing people who had no idea about reality such as the economy" – and points to their preponderance of economists, including himself, Vince Cable and Mr Laws. He believes Mr Laws should not have resigned over the revelation that he had paid £40,000 in parliamentary expenses in rent to his partner and, in fact, that he will return to government soon.
But there is a wider challenge, beyond rehabilitating the Lib Dems, and Huhne is clear about the dangers that lie ahead in the effort to reduce the deficit. Like all his senior colleagues, he immediately answers "five years" when asked how long the coalition will last. But he also conceded: "I'm not sure that in 18 months' time we're going to be the most popular government this country has ever seen – in fact I very much doubt it.
"And that will also in a funny way yoke us together until we can get through and show people there are real improvements, that we've dealt with the problem, and they can now look forward to the sunlit uplands and that the recovery is there."
1954 Born, 2 July
1972 Sorbonne, Paris (Certificate French language and civilisation)
1972 Magdalen College, Oxford (BA philosophy, politics and economics).
1975 Worked as undercover freelance journalist in India during Indira Gandhi's emergency, when Western reporters had been expelled.
1975-94 Journalist, at Liverpool Daily Post, The Economist, The Guardian, Independent and Independent on Sunday.
1984 Married Vicky Pryce (one daughter, two sons, two stepdaughters).
1994-03 Company director.
1999 Elected Lib Dem MEP for South East region.
2005 MP for Eastleigh. Shadow chief secretary to the Treasury.
2006 Runner-up to Menzies Campbell in leadership contest.
2007 Lost leadership contest to Nick Clegg by only 511 votes.
2009 Expenses revelations showed he claimed for groceries, fluffy dusters and a trouser press. Said he needed the press to "look smart" for work, but repaid the cost.