The mayor of London isn't much of a boxer, but the man can surely skip. The second half of this I see for myself, by the ring in Earlsfield Amateur Boxing Club, south London, as Sadiq Khan takes his jacket off and bounces up and down for the GQ cameras, shirt and tie still intact, black leather shoes slapping on the floor. The first bit I get from his brother Sid, who is the club's head coach. Though maybe I wasn't meant to pass it on.

He looks just like Sadiq, does Sid. You walk in and the first thing you think to yourself is, "Oh, there's the mayor of London, but he's beefed up and put on a tracksuit." Sadiq, Sid and their other five brothers (there's also a sister) all used to box here from the age of eleven. To use the parlance of south London, this is his manor. The Henry Prince Estate, where they all grew up, is half a mile down the road. Everybody knows his dad was a bus driver, because he says it so often it has almost become a joke. Here, though, it really does seem pertinent. The No44 bus, which he drove, brought me here from Tooting Broadway Tube station.

See Sadiq Khan give GQ a tour of Earlsfield Amateur Boxing Club

Browse the photos on the wall here in this gym and you'll spot Khans aplenty in faded snaps and newspaper clippings of teenage triumphs. Sadiq himself is in a few, but he's normally a bit older, maybe an MP by now, come back to present a trophy to some skinny kid in a vest. Even now, when he walks around there's a strong vibe of local boy done good. It's possessive, though, rather than awestruck. Trainers slap him on the back. Kids in the ring nod at him and he nods back.

"Oh, listen," he says, when we sit down toe-to-toe by the ring upstairs, like chess boxers doing the chess bit, "there's no airs and graces about it. There is that sense of 'our boy's done well'." When he goes to the mosque on Fridays it's the same. "Yeah you get the odd person who wants to take a selfie. But the vast majority of people couldn't give a monkey's. As it should be." It keeps him anchored, he says. Keeps his feet on the ground. "Because otherwise?" he shrugs. "Listen, you do get delusions of grandeur. It does go to your head. Because, you know, it is quite... fantastic."

Listen, you do get delusions of grandeur. Because, you know, it is quite...fantastic

Sadiq Khan is not just a mayor. Sadiq Khan is a choice about what London wants to be. Which is not just me gushing, by the way, because I'll be mean enough in a minute. It's just an observation. This son of a south London bus driver (had you heard?), this first-generation Brit, is the first Muslim to lead a major European capital. He has a bigger personal mandate than anybody else in British political history, bigger than that of any other Muslim in the Western world.

"I didn't really appreciate the impact of that election," he says now. "I really didn't. We were walking towards the count on Friday, and I saw the international media pack, and I still... didn't quite get it. And it was only when, a few weeks afterwards, when, you know, Christiane Amanpour wants to interview me. I'm not name dropping. But, you know, all these people around the world. You've got Justin Trudeau ringing me, not just other mayors. You think, something is going on here. People were saying to me, senior journalists, 'I've just been on holiday and they were talking about you in a village in Cambodia.' Something is happening."

© Getty Images

Even Donald Trump took note. Then just the Republican frontrunner, Trump was still telling people he planned to ban all Muslims from entering the United States. "There are always exceptions," he said, magnanimously, of London's new mayor. We'll come to that in a bit. The point is, if 2016 was the year of divisive political campaigns - Brexit and Trump being the obvious examples - then Khan's election was the one that went the other way.

During that election, the Conservative Zac Goldsmith called him "radical", "divisive" and "a real danger". He accused him of "pandering to extremists" and of "ambiguity... when it comes to keeping Londoners safe". Labour MP Yvette Cooper wrote in the Times that Goldsmith's "subtle dog-whistle" had turned into "a full-blown racist scream", and I'm not wholly sure she was wrong. Though London, in the end, wasn't having it.

I don't know what happened. One day Zac Goldsmith stopped talking to me - it got nasty

"Can I just say this about Zac Goldsmith?" says Khan now. "Before the campaign began, I said publicly what I felt privately, which is that I was hoping he was the Tory candidate. Why? Because I'd got to know him in parliament. He's a nice guy. And at the beginning of the campaign, he was still the Zac I know."

In the green room, he says, when you're off-camera, "You get on with Tories. Then you do the debate - fisticuffs, verbally - then again afterwards. It's theatre, right? And something happened. I don't know what. Maybe one day Zac will tell us. But one day..." he clicks his fingers, "...he stopped being friendly. Stopped talking to me. No eye language. It got nasty and horrible."

Khan says now that he's still not sure whether Zac grasped the impact of the language he was using. "There are so many people who feel the ripple effects of that campaign," he says, "and I'm not sure that Zac fully appreciated that." He brings up, unprompted, the fact that Jemima Goldsmith, Zac's sister, has Muslim children from her marriage to Imran Khan. "Zac has got nephews who are going to experience some of those consequences," he says, "his own sister. So I find it difficult to understand."

President Trump will see the best of London, and that includes ethnic-minority London

The funny thing is, this is Sadiq Khan we're talking about. On the one hand, he's a totemic trailblazer for the future of European social integration. On the other, he's a malign sleeper Islamist menace. "And he's only Sadiq Khan!" is how one Labour insider puts it. "A mid-ranking Milibandite! How the hell did that happen?"

I spoke to a handful of Khan's former colleagues and rivals in the Labour party while writing this article, some on the record and more off it. All of them wish him well, if only because it must be nice, in these dark days, to have at least part of your party not be a farcical disaster. Almost universal, though, was a sense of mild bemusement. The magnanimity, the public popularity, the global relevance: nobody saw them coming. Some liked him and some really didn't, but nobody thought he was that kind of guy.

"We all thought he was a bit slippery," says one. "Mercurial," says another. "A bit 'all things to all men', although not a showboater. He's rarely attracted attention when he has not wanted to, which is actually quite a skill."

Several, though, tell me that Khan went for the mayoralty like they'd never before seen him go for anything. David Lammy had already thrown his hat in the ring and remembers asking Khan for a meeting after the rumours began. "I looked him in the eye and I said, 'Look, Sadiq, what are you going to do?' and he said, 'I'm going to run and I'm going to win. And I thought you should know that.'" Lammy laughs, incredulously. "He hadn't even declared at that point. I had a lot of respect for him."

Others describe him, equally startled, as Ed Miliband's greatest legacy. "Ed didn't have many mates," says one, "just Sadiq and Chuka [Umunna] really. So he played a blinder in exploiting that." Within the party, in fact, there is a narrative which sees Khan's internal ascension as very much in the mould of Ed Miliband's. Labour is a tribe, they say, made up of other tribes, and he knew exactly how to navigate them all.

Diane Abbott, another contender, expected the backing of the unions, and particularly Unite, but Khan beat her to it. "Diane was really pissed off," I'm told. She also might have expected the love of the Corbynistas, but Khan, who had helped Jeremy Corbyn onto the ballot in 2015, successfully courted them too. And lo, when the final internal showdown came, with Khan versus Tessa Jowell, the dynamic was really that of Ed versus David Miliband all over again. Jowell was the centrist, the experienced politician. She'd brought the 2012 Olympics to London and for any outsider was the obvious choice. But Khan had worked the machine.

Unlike Miliband, though, he was ruthless enough to win the final election too. When Goldsmith described him as "Corbyn's man in City Hall" Khan pointedly distanced himself from his own leader, both by criticising him for not singing the national anthem and for his failure to combat anti-semitism. When he was finally sworn in at Southwark Cathedral, Corbyn wasn't even there.

If you can't win a leadership contest and defeat Jeremy Corbyn, how do you realistically think you're going to win the next general election?

This, many say, is a bit of a pattern for Khan. As an MP, he was pro-Heathrow expansion. As mayoral candidate, he was against. "He's not a conviction politician," is how one former colleague described it, putting it nicely. "He's a pragmatist." Still, it seems to work.

© Getty Images

I do enjoy the rough and tumble," says Khan now about all of this. "But I enjoy achieving things far more. Look, I was an MP for eleven years. And I felt I achieved more in my first five than my last six. Why? Because we were in power."

Anyway, he says, it's different when you're mayor. "Only a small part of my job now is tribal politics. A lot of it, and I say this not in a pompous way, is above party politics." Some in his party, he says, might call him "a sellout" for cooperating with Tories and big business. Though, as he sees it, "It's getting things done for the city that I love."

Khan backed Owen Smith in the Labour leadership election of 2016 and his relationship with Corbyn, who won, remains grim. Still, if he regrets nominating him in the first place, he won't admit it. "We lost the election of 2010 badly," he says. "We lost again in 2015. And the idea, in those circumstances, that the membership should be denied an opportunity to discuss how to win back power? I don't think so."

London made my family and myself

Well, yes, sure, but it doesn't seem to be turning out swimmingly, does it? He shrugs.

"The reality is - and I say this in a fraternal spirit - if you can't win a leadership contest and defeat Jeremy Corbyn, how do you realistically think you're going to win the next general election?"

Put on the spot, he honestly doesn't seem to know what Labour should do to win back power. Reading between the lines, I'm not actually sure he regards it as particularly his problem. Or at least not yet.

Originally he wanted to be a dentist. His A-levels were all in science and maths. Eventually, though, partly as a result of a maths teacher telling him he was good at arguing, but partly just because he really liked watching LA Law, he decided to be a lawyer, instead. Out of eight siblings, he says, seven went to university. He went to the University Of North London.

"It was very political," he says. A few years earlier, there had been a big fight over a guy called Patrick Harrington, a student, who was a member of the National Front. Other students picketed his lectures. There were sit-ins. It was the Eighties. Things were different.

© Rex / Shutterstock

"When I was growing up," he says, "anyone who wasn't white was black. It meant all of us. Though when I was at university, we started to be called Asians. Then the politicisation of faith only happened during the Rushdie affair, which was around that time, and suddenly people were calling us not black any more, or Asians, but Muslims. And it was peculiar. It was identity politics. It was all changing."

He wasn't into any of that stuff, he says. He'd joined Labour when he was 15 and gone to one meeting and then not gone back for two years because he didn't understand what was going on. His father, the bus driver ("Have I mentioned," he asks, eyes twinkling, "that he was a bus driver?") was Labour, but not politically active. He always read a broadsheet - the Telegraph or the Times - but that was it. "We were blessed" he says. "Everybody worked. I never saw anybody going out to work in a suit, but they were in uniforms - bus driver, train guard, in a factory. Everyone was working."

He calls it "the London story", the idea that "you work hard, you get a helping hand and you can achieve anything". In the Khan family's case, that helping hand meant a council house and good schools. "I can't remember people being on benefits," he says, perhaps dangerously, "because there was a work ethic."

I've spent my entire adult life encouraging minority communities to get involved in mainstream society

Nor, contrary to what Zac Goldsmith might have had you believe, did he grow up with a sense of burning injustice, or even any particular anger towards the system. He remembers a school sports event being cancelled because of industrial action and a period where his dad's job (he was a bus driver) looked like it might be under threat. Once or twice, he remembers the older brothers of friends being stopped and searched.

"It felt unfair," he says now, with a shrug, though that's as far as he'll go. "London made my family and myself," he says. "You know, we've got cousins in Pakistan. They're ethnic majority and religious majority. We've got cousins in India. Ethnic majority, religious minority. And they say to me and my family, 'We couldn't have done in Pakistan or India what you've done there.' Which is, you know, well the 44 bus you see outside was driven by my dad and..."

Yes, I say. You said.

After university he went to law school in Guildford and became a solicitor. When his opponents want to link him to dodgy people, this is the time they focus on. Lots of his work involved actions against the police. Often, there was a race angle. Occasionally, there was an implied faith angle, as with the case in 2001, in which he successfully fought to overturn a ban on Louis Farrakan, leader of the Nation Of Islam, from entering the UK. Eventually Khan became the chair of Liberty and recruited Shami Chakrabarti.

© Rex / Shutterstock

By this point, many of his cases involved actions against the government of Tony Blair. Or, as he puts it, "There was a tension between the views I had and the things the Labour government were doing." In 2005, he became a Labour MP anyway. A year later he was a signatory, and some say the orchestrator, of a letter criticising Blair's policy in the Middle East. Two years after that, he was bugged by the Metropolitan Police while visiting a constituent, Babar Ahmad, who was being held in prison on terrorism charges. There was quite the fuss at the time, not least because it's illegal to bug an MP. Moreover, one rather suspects it might not have happened if he hadn't had a name like Sadiq Khan.

During Ramadan, I fast. I give money to charity. I try to be good, although I don't proselytise and I don't make a song and dance

"I made a conscious decision at the time not to make a big song and dance about it," he says now. "Let me tell you why. I've spent my entire adult life encouraging minority communities to get involved in mainstream society, civic society. And I don't want to start telling you my war stories. The racism I experienced as a lawyer? How can I encourage you, as a young Asian, a young African Caribbean, a young woman, to become a lawyer if I'm telling you how horrible it was? Sure, people were telling me, and I'm being diplomatic, 'For goodness' sake, if they're bugging you what chance do we have?' But if you make a big song and dance about it, you are inadvertently putting people off."

Look across the Atlantic, and not just across the Atlantic, and you will find those who truly think what Zac Goldsmith was hinting at, that Khan is representative of a wave of Islamisation, sweeping Europe. He's on his firmest ground, I think, when he explains precisely why they are wrong.

"The reality is," he says, "there is a narrative that so-called Isis and Daesh have. And their thesis is that it is incompatible being a Muslim and a Westerner, that it is incompatible to have Western liberal values and to practise the faith of Islam. And what breaks my heart is when you've got sensible people, who should know better, playing into that thesis."

Sensible people like Donald Trump? He grimaces. When Trump said that London's new mayor could be an exception to his Muslim ban, he reminds me, his response was to invite Trump to London instead. The invitation still stands. "Absolutely," he says. "The president should come to London. There shouldn't be a state visit. What I hope happens is that the PM rescinds the offer of a state visit until the ban is lifted. But if there is going to be a visit, I'm going to make sure President Trump sees the best of London and that includes ethnic-minority London. I want him to meet the greatest sportsman ever, Sir Mo Farah, and..."

© Getty Images

Really? He'd take Donald Trump by his tiny hand and lead him to Mo Farah?

My family has married people from all sorts of different ethnic backgrounds

"Oh, I'm not sure I'd hold hands," he says quickly. "That's for others to do. But I'm looking forward - and I say this not in a patronising way - to educating him. Because I think he recognises, in his private moments, that the way you campaign and the way you govern are different."

For Khan, though, I'm not sure they were. If there has been a shift, between the "slippery" machine politician he used to be and the magnanimous London incarnate he now considers himself, then it seems to have happened during the campaign itself, in opposition to Goldsmith. Though in fairness, the signs were always there.

"I've always been impressed how pro-gay he's been," says Chris Bryant, the Labour MP. "Never a shadow of doubt. And when I hear somebody say, 'We don't want a Muslim mayor' for reasons like that, I want to say, 'No, you've got it badly wrong.'"

Khan's faith is, I suspect, more central to his life than he quite likes to say. "I pray," he says. "During Ramadan, I fast. I give money to charity. I try to be good, although I don't proselytise and I don't make a song and dance."

London is about Jews, Christians and Muslims coming together

He and his wife, Saadiya, also a solicitor, raise their two daughters as Muslims. They're both teenagers now. And if they wanted to marry outside the faith? "It's a choice for them," he says, "when they're adults. Look, my family has married people from all sorts of different ethnic backgrounds. It's one of the great things about London. How we evolve, in relation to identity. My mum's got 24 grandchildren. Three great grandchildren. Lots of different ethnicities. My children have been raised Muslims, but you have to wait and see what happens."

During his campaign, he made a point of reaching out to London's other religious communities, turning up in synagogues and gurdwaras, embodying the idea that one minority is much like another. Speaking personally, as a wholly secular Jew, that stuff counts for a lot. When Ramadan began last year, he was to be found at Lambeth Palace, posing for a selfie with the archbishop of Canterbury and the chief rabbi. "That photograph went viral," he says, very proudly. "It does so much good. Showing that London is about Jews, Christians and Muslims coming together."

There's a strong streak of myth-building about Sadiq Khan and I'm not sure he always knows he's doing it. While running for mayor, for example, he claimed that Blair had called in Labour's four Muslim MPs, after 7/7 and told them that Islamic terrorism was their responsibility. "I said, 'No, it's not,'" was how he reported it. "'Why have you called us in? I don't blame you for the Ku Klux Klan.'"

I feel like the boy with the golden ticket, I've got the best job in the world

Shortly afterwards, Khalid Mahmood and Shahid Malik, who would have been two of the others, disputed his account. "Khan's depiction of his bravado is almost comical" they said in a letter to the Guardian. It's a very Sadiq Khan story. As in, you badly want it to be true. It would be terribly fitting if it was. Only, I'm not sure it is.

What you sense now, though, is a man set upon living up to his own myth. Really, Goldsmith did him a massive favour and Trump has too. Without them, he might still be the machine Labour politician, Mayor perhaps, but not for any special reason. Watching him on television during the Blair years and the Gordon Brown years and, frankly, the Miliband years too, he always seemed quite an angry figure, rolling his eyes, almost petulant. There's none of that any more.

These days, it's all about transcending division. He mentions several times, for example, how proud he is of working with Sajid Javid, the Conservative communities secretary, who is also the son of a Muslim bus driver. ("You wait ages for one," Khan quips, "and then two come along at once.") He's also proud of working with the police, who are the same police he used to sue. "How difficult their job is," he says, "the risks they take. You see it in movies and think, you know, police officers rush towards danger. And they do! I meet these people every day. You learn a new respect."

Will the glow last? Maybe, maybe not. Some in Labour believe the unions will turn on him before long, regarding him as a sellout and a disappointment. Though I reckon he might turn that one to his advantage. A greater risk might be hubris. "Actually, I went to the United States recently," he says, at one point. "Met with Rahm [Emanuel] in Chicago. And Bill [de Blasio] in New York. And the Clintons. And Trudeau in Montreal. And people say, 'If London can do this...' And I'm not comparing myself to Barack Obama! But people are like, 'We elected a minority, but he's not a religious minority!' And so..."

And on it goes, although thus far you can forgive it. Mainly, he's just delighted. "I feel like the boy with the golden ticket," he says, quite openly. "I've got the best job in the world." As to what he'll be in four years time, let alone eight, well who knows? As I leave him, and Sid too, and head back to Tooting Broadway on the 44 (which his dad drove, by the way), my strong hunch is that he won't stop at mayor.

Yes, he skips around and, yes, he fights a little dirty. Pull it all together, though, and he reminds you of an optimistic time that all the worst people in the world want us to forget. A time before multiculturalism was a dirty word and before "left of centre" meant Jeremy Corbyn. And if you miss that world, and God knows I do, then Sadiq Khan doesn't half pack a punch.

Hugo Rifkind is a writer for the Times.

Like this? Now read:

Hey, Donald Trump, back the f**k off our mayorA gentleman's guide to the political party manifestosTony Blair to Alastair Campbell: 'I'm still basically optimistic'