Boris Johnson: Could I have a word, Boris?

We sat by the river, drinking beer. He cracked clever jokes, quoted ancient Greeks and confessed to knowing not very much about policy. "Common sense, that's the thing!" Boris the blond bombshell, the wit and telly star, was on brilliant form in the sunshine, not seeming to care what he said on the campaign trail. "Ripper!" But that was seven years ago, when he was about to become MP for Henley. Where is he now, that carefree maverick?

All over London, of course, pressing the flesh as he attempts to become mayor on 1 May. But while the white-gold mop top on the TV news is the same, the man underneath it isn't much like the one I remember. The wisecracks have been replaced with policy statistics. The cheeky, schoolboy grin has become a jowly, pugnacious scowl.

Boris has gone serious, under the influence of the political strategist Lynton Crosby, with a "scary" – his word – PR team hired to ensure he avoids making another huge gaffe (like offending the entire city of Liverpool). So has the real Bozza gone into hiding, or has the genuine Boris Johnson emerged at last in this growling, hard-talking candidate, daringly unafraid to bore?

There are other questions to ask, too. On one very important issue, I suspect him of being as evasive and careerist as any politician – even his rival, Ken Livingstone. I would love to ask him about it, but that's proving very difficult.

We have requested an interview several times, going back months, and been stalled. I logged on to his website, as any Londoner can, simply asking where to hear him speak. That was ignored. I even contacted his campaign on Facebook.

His team says he is far too busy. Anyway, it has recently emerged, they don't like this newspaper. Why? Purportedly, the gifted comic had a sense of humour failure when something we did "angered him a great deal". Last month, The Independent on Sunday summarised the candidates' policies, best and worst moments, etc. One question asked: "If you fail, what will you do?" We quoted Ken Livingstone as saying he would retire from politics, but for Boris, we imagined he would bounce back in the media and "continue to add to his collection of gaffes". A bit cheeky, admittedly, but hardly over the top in the rough and tumble of politics.

Other journalists have also complained that it is hard to get a proper interview with Boris unless your publication backs his campaign. But even Quentin Letts of the Daily Mail, a friendly face on the trail, says Boris looks "pooped" and has "dropped much of the horseplay".

I'm not giving up, though. Wednesday night and he is at a hustings near Trafalgar Square. He does indeed look pooped, but no wonder. Boris has already parlayed with the meat porters at Smithfield in the early hours, schmoozed City bigwigs in Broadgate and pumped HP sauce on to a full English at Leadenhall Market. Now, in the early evening, he is at the grand church of St Martin-in-the-Fields. Given two minutes to set out his stall, he says: "I don't want to be remotely confrontational in this holy place ... but I do think it's time for a mayor who concentrates on the issues that really matter to Londoners, and that is our housing and our transport system, and crime and fear of crime."

Later he lashes Ken for "being nannying and interfering", and says London taxpayers are angry at their money being "trousered, or worse, by the associates of the Mayor".

Question time. I write my query on a card, but it doesn't get chosen. I thrust my hand into the air, give a big smile and don't get called. My question is simple: when did Boris stop being a climate-change denier, and why?

His campaign is in line with new Tory orthodoxy – but in a column eight years ago, Boris wrote that the "eco-warriors' case [against cars] is nonsense". He said: "There is no evidence that the planet is suffering from the extreme weather patterns associated with climate change."

The change seems to have come in early 2006. In February that year he described fear of climate change as "like a religion" and confessed his mind was "bubbling with blasphemous thoughts" – but said he "couldn't possibly disagree" with the new faith. Why not? Four weeks later, he confessed: "I am far too terrified to dissent from the growing world creed of global warming."

Terrified of what, exactly? Losing his job? Boris was brought into the Shadow Cabinet by Michael Howard, who sacked him for lying about an affair. He was restored by David Cameron just before Christmas 2005, and given one last chance of a serious political career. But the new boss was a recycler, an erector of domestic windmills. Is it possible that Boris doesn't really believe in climate change at all but had to go along with what he used to condemn as guff, so as not to be consigned to political oblivion?

If that's true, what does it mean he will do once elected? His manifesto is big on preserving London's green spaces, but at the meeting he sticks to his old line that cars are not as much of a problem as "commercial and domestic emissions from boilers". He gets vigorous applause – from just one pew. "Only your team clapped," points out the host. "Quite right," admits Boris. "I'm very grateful nonetheless."

He dismisses the Mayor's £25 charge on gas guzzlers as ineffectual. "The total reduction would be roughly the equivalent size herd of cows, per year."

The people in my pew leave confused, having hoped for jokes. But he has told the Evening Standard: "I simply cannot afford to give the media any sign that I'm not taking it seriously." He's right, of course. The Mayor will control a budget of £11bn, and you can't do that with a tickling stick. But still, wit and irreverence are what got Boris where he is. Many of us wait to talk to him afterwards, but he slips out through a side door. Back home to Islington, presumably.

Next morning, Alexander Boris de Pfeffel Johnson is serving his leader, accompanying Mr Cameron to meetings that emphasise how seriously the Tories take crime. I call his PR people early, to ask for just five minutes with Boris today. It's unlikely, a spokeswoman says. Someone will call me back. They don't.

From an early start at police support headquarters in Lambeth, the dynamic duo must journey north to the Jill Dando Institute at University College London. Will they cycle? I take the Tube and wait outside. It's 10.07am, and I recognise a slender, shaven-headed man from last night. This is it. A silver car drops off Dave and Boris, both in dark suits. They used to look like an odd couple, but now they're like a couple of mid-ranking detectives arriving at a crime scene. The Old Etonian and, er, the other Old Etonian. They're inside within moments, so there's no chance even to call out a question. Not having the benefit of a chauffeur, I tramp through puddles to the station, heading for Westminster.

At Local Government House in Smith Square, they unveil a new scheme for online crime maps. Bozza and Dave – as he keeps calling his leader – sweep in late. Boris apologises to the massed ranks of the media: "An articulated bus was stranded like a beached whale across Kingsway, impeding our progress."

Everyone wants to talk to him afterwards. I wait in line behind the BBC, then LBC, then another camera crew, and another, then a correspondent from Italy that Boris obviously knows. He speaks Italian, and they laugh. "Is it Cole?" says Boris suddenly, looking up in mid-stream. Yes, I say, taken by surprise. He smiles, and returns to the Italian, who has just asked about his reputation as a clown. "I don't think anybody underestimates the seriousness with which I am approaching this job."

Indeed. I am next, and the only one left ... but just as Boris opens his mouth to speak, the handler places his body between us. They have to go, he says nervously but insistently. Right now.

"Cole was with me on the stump in my first campaign in Henley," Boris protests. The old pro has either been forewarned, or this is an example of that prodigious memory that allows him to quote the Greeks at length.

"Cole is my first priority!" he insists, not entirely plausibly, but the handler has other ideas. Al-Jazeera has appeared. Suddenly, it seems, they are not in such a hurry to go. Boris tells the reporter he is proud of his Muslim ancestors, rattles off a few answers then turns back to me. The room is almost empty. Every single reporter or broadcast journalist who wants it has been given time. But not me.

"We really do have to go," insists the handler, who has obviously had firm instructions not to let us speak. Boris shrugs, and flashes one of those smiles that have helped him get away with so much. He's sorry, he's so busy, he'll ring me. In the morning. Absolutely.

I know he won't. Even if he wants to. (And so, in time, it proves.) As he is led out of the door, Boris reminisces, briefly, about that time we drank pints of Brakspear in Henley. "That was a good day," he mutters. "I remember it well." He ruffles his hair. He looks exhausted. "God," he says, meeting my eye, "it was all easier then, wasn't it?"