Ed Davey is running for the Liberal Democrat leadership and it’s all the fault of an advert in the Guardian. Having newly graduated from the University of Oxford in 1988, Davey had hoped to do an MSc in agricultural economics and work in developing countries, “because climate change and global poverty were the two biggest issues in the world”. He applied for a grant at the Ministry of Agriculture Fisheries and Food (now Defra), but was turned down.

“It wasn’t very well thought through, I have to be honest,” he says when we meet on a train to Stockport en route to a campaign stop, where he will meet and talk to Liberal Democrat members. He launched his campaign the morning of our interview, and he takes off his tie with great relief as we sit down. Davey is an easy, compelling speaker who rattles off his life story with good humour, telling me how, having been turned down for the grant, he applied for a series of jobs, one of which was a position advertised in the Guardian for an economic researcher at the newly merged Social and Liberal Democrats.

He wasn’t even a member of the party and took advice from one of his tutors, the then little-known academic and former councillor Andrew Adonis, about whether the application was a good idea. Adonis told him he wouldn’t be “burning bridges”, and so Davey put in his application. “I was surprised to be shortlisted,” he says. “I was completely bamboozled to get the job.”

Davey had been interested in politics from a young age, and recalls, aged 12, being taken to a Young Conservatives disco by his older brother, an experience he says “put me off the Tories for life”. But beyond what he describes as a sense of being “vaguely anti-Conservative”, his own politics were loosely formed until, in his late teens, he read Jonathon Porritt’s Seeing Green, which along with James Robertson’s The Sane Alternative and the work of the economist Paul Ekins are the books he cites as shaping his thinking.

While studying PPE at Jesus College Oxford, he was a member of the Student Ecology Group, which he later managed to get renamed Green Action in what he calls “my first bit of political spin”. Consciously or not, he was emulating Porritt, who, the same year that Davey arrived at Oxford was instrumental in the Green Party’s own rebrand: changing its name from the Ecology Party to the movement we know today.

As far as Westminster politics were concerned, during his student days Davey’s focus was on a tactical voting campaign called in 1987, where local residents tried to get a Labour MP elected in Oxford East and an SDP-Liberal Alliance MP in Oxford West, succeeding narrowly in the former, but falling short in the latter.

Porritt is in many ways the founder of the modern Green Party – so why didn’t Davey join?

“I always thought that would be where I ought to go,” he confesses, “but I found their thinking fundamentally not very clear and not very attractive, because some of it seemed very authoritarian, and then some of it really left-wing.” Davey knew that he was “a liberal economically, socially and politically, but [I] hadn’t quite made the journey to the Liberal Democrats”.

As leader, would he be open to a nation-wide pact with the Green party? “I’m all in favour of talking to other parties, always have been, always will be. I’m a pluralist, talk to them, see what we’ve got in common, work together, fine. But doing electoral pacts is a big step, and I have concerns both in terms of the voters – you know, stitching it up for the voters to have a say, I worry about that.”

I ask what the difference between that and Tactical Voting 1987 was.

“Tactical voting is grassroots: the people are doing it,” he responds. “I think that bottom-up thing is really very important. I think if it’s top-down, it is a stitch-up – it is trying to get in the way of the electorate.” So no to pacts, but yes to tactical voting?

“Never say never” is his verdict on both. “The climate change emergency is so great that if there are things that we need to do together to make sure we address that, we have to go the extra mile.”

“But I do feel a bit like over the Remain issue, where we proved beyond doubt that we were the leading Remain party by a long way, and we got Remain votes behind us and I would argue on climate change, we are the climate change party, and people should get behind us, because we’re likely to win many, many more seats than the Greens are. I don’t know what the Greens’ top number they can win is, but it’s a lot lower than ours. And I think we have a chance to break through, even under first-past-the-post, in areas that the Greens would struggle. So, if you think the issues out there are about Brexit and about climate change, the Liberal Democrats are the vehicle for those policy areas, and my strategic plan wouldn’t be some deal with the Greens.”

He explains that his reticence to join was that he found the alliance between the Liberal party and the Social Democrats “a bit wishy-washy, a bit unclear”. I ask if that memory influenced his scepticism about a merger or alliance with Change UK, something that other Liberal Democrat MPs, including his leadership rival, Jo Swinson, were more open to.

“It’s more to me to do with Change UK, to be honest,” he says. “I had huge respect for them taking the courage to leave their own parties, I can’t imagine doing that and it must have been very difficult for them, and clearly we should work with them, because they want to stop Brexit, and we’ve got that in common, but when I looked at them, having worked with a number of them over a number of years – people I like – I just thought, ‘Well, I’m not quite sure what else you have in common, let alone what you have in common with us’.”

“Some of them clearly do, some of them are liberals in the wrong party, that’s for sure, and I hope they will come across.” Davey, who I spoke to before Chuka Umunna’s defection to the party, singles Umunna out as one he believes will be comfortable in the Liberal Democrats, but says “I think for others, it will be quite difficult. I mean, I’m not saying we can’t be open-minded and be an open church, if they come across fine, I just didn’t think that it looked very plausible. You can’t make big decisions about a party, for all that it matters, on the basis of five minutes of good headlines, you’ve got to be way more strategic than that. Our party’s been around in one form or another for longer than any other party: liberalism is fundamentally important, you don’t water it down because there’s a few people who’ve left their parties and they’ve got this new thing which no one knows if it’s going to go anywhere.”

What if it had been more successful, draining oxygen from the Liberal Democrats? “I never felt that risk was that great; I never got the sense,” he responds. It would be different “if Tom Watson decided to take his lot from Labour” but, Davey adds, “I don’t think [that] is going to happen”.

In January 1989, it was working for the party, and meeting Paddy Ashdown for the first time, that changed Davey from liberal to Liberal Democrat. Ashdown, who died last year, had at that point been leader for six months; in later life, he was fond of telling people he’d taken over a party that was polling so badly it was “represented by an asterisk” – that is to say, within the margin of error for having no support at all. Ashdown hadn’t yet wholly revived the Lib Dems, but he won over Davey. “I just saw Paddy and thought, ‘This guy is the bee’s knees.’”

He was working on economic policy for Ashdown and completing his masters in the evenings at the same time, helping to devise and cost policies like the party’s pledge to raise income tax by a penny to fund education, or to grant the Bank of England independence, a policy that would later be adopted by Gordon Brown.

Shortly after the 1992 election, Ashdown asked him if he would think about becoming his chief of staff. “I sort of by that time was beginning to feel like I might stand for Parliament, but I sort of felt I needed to get out of Parliament,” he explains, so he instead took a job at a management consultancy in Chiswick by the name of Omega Partners. He tells me he learnt two things from his time there: the first was the intricacies of how different countries’ postal systems worked and the second was “to think very carefully before you embark on management consultancy”.

Missing life at Westminster, he decided to go for parliamentary selection earlier than he’d planned. He missed out on the candidacy in Twickenham, the party’s number one target in London, to a little-known economist by the name of Vince Cable, but was selected for Kingston and Surbiton, the party’s 106th most winnable seat.

“Some people said ‘This is a three-election seat, you’ll never win it’,” he recalls “But there were some really good campaigners out, had some lovely, lovely people who’ve become close friends. We’d won the council in ’94 and I just thought, “Well, might as well go for it”.”

He was still working as a management consultant travelling around, but would campaign every weekend and free evening. “It did that for two years and, and it was not good for my health, and by the time of that election I was probably more unwell than any other time.” Davey believes that his victory – he won by 57 votes after three recounts in 1997 – was only possible because he was single and childless, which he singles out as a major problem in increasing participation in politics.

Davey describes himself as “like a Labrador puppy” in his first parliament, so excited was he to have been elected. His main focus, given his 57 vote majority, was winning over the people of Kingston and Surbiton, doing constituency surgeries and working the seat hard. “The Tories said I’d turn up at the opening of an envelope, which wasn’t quite true, but you could tell I was getting to them.”

The strategy worked and in 2001 Davey was rewarded by the largest majority ever achieved by a Liberal Democrat in absolute terms. He became local government spokesperson for the party, working on their campaign to scrap council tax, where he first met his now wife, Emily Gasson, who he describes as “Liberal Democrat to her core”. During our interviews, he lights up with pride twice: the first is talking about the forward strides made on renewable energy in coalition, the second is talking about Gasson’s work as a councillor.

Davey endorsed Nick Clegg in the 2007 leadership election, and is still a supporter of the deputy prime minister. “I thought he did a really good job. He struggled to start off with: all leaders struggle, because we don’t get that much media, you know? Nick was two or three years in and they’d go down the high street and they’d say, “I’ve just shown your photograph to 110 people, Mr Clegg, and no one knows who you are”. And that just comes with the territory, I guess. But then he did his amazing performance in the 2010 election and we got the zeitgeist and the rest is history.”

Despite their ideological closeness, Davey had to be content with a junior ministerial role at the start of the coalition. “I think I may have annoyed him a little bit, because during those famous five days [when the coalition was being negotiated], I had sided with Paddy, in the sense that we should take seriously talks with Labour.”

It was his stint as a junior minister under Vince Cable that he cites now, in arguing for the value of coalition rather than a looser confidence and supply deal than the one pursued by the DUP since 2017. “I taught me that lots of political decisions are taken that no one ever really gets to hear about and they can be really important.” He was closely involved with the privatisation of the Postal Office, which he believes was a necessary prerequisite to get the investment into postal services to turn them around.

He was judged sufficiently capable to earn a promotion to the Department of Energy and Climate Change, where the National Audit Office criticised him for spending too much on wind power, a decision he still defends now, arguing that without the government making a big outlay the price would never have dropped. He believes that decision has changed the calculation as far nuclear power, which he backed in coalition, is concerned. “While the costs of onshore and offshore [wind] and solar have plummeted, the costs of nuclear have not,” he says, “The future of nuclear is bleak.”

It is that record that makes him so loud and proud in defending his time in coalition, unlike his rival, Jo Swinson, who has talked about the need for the party to “own the failures”. But his is party willing to elect a man who is unrepentant about its time in coalition? “We’ll see,” he says, as the train arrives in Stockport and he heads off to make his case to Liberal Democrat members.

A shorter version of this interview appeared in the New Statesman's print edition, and can be read here.