I meet Sadiq Khan in his campaign HQ in Westminster. We’re in a side-room littered with half-empty boxes of leaflets, piles of upside-down placards and a dusty portrait of Clement Atlee. One of Khan's aides rushes around straightening the room up for our camera. Soon the candidate walks in fresh from a campaign visit to Deptford. He seems friendly and confident but not entirely relaxed. The first thing he asks is how high I believe turnout will be. While all the public polls have shown Khan with a healthy lead over his rival Zac Goldsmith, Labour are worried that a low turnout in inner London could benefit the Tories and rob Khan of victory. Both Labour and Tory activists have reported widespread disinterest among voters on the doorstep.

This voter apathy has been compounded by Goldsmith's attempts to link Khan to Islamic extremists in an attempt to depress his support among Labour voters. In recent weeks senior Conservatives have accused Khan of associating with supporters of IS, labelled him "radical" and even suggested he supports Sharia law. Goldsmith, whose personal dislike for Khan has become increasingly apparent, has described him as a "real danger to London".

Labour, in turn, have accused the Conservatives of "dog-whistle" racism and a campaign which is a "racist scream". As a result, a contest which once promised to be dominated by questions on housing, transport and air quality has instead focused on race, religion and extremism.

Khan says he has been surprised at how Goldsmith has run his campaign.

"To be honest, I'm disappointed," he tells me.

"I've come across Zac Goldsmith before he became the candidate. He's a nice bloke. He really is a nice bloke. He's charming, he's personable, he's interesting. Before he was selected I was asked publicly on a couple of occasions about the Tory contest and I said I hoped it was Zac. Why? Because I thought we would have a great campaign fizzing with ideas. We would be competing about the battle of ideas over the vision for our city. I'm disappointed by his campaign. I think it has been negative. I think it has been divisive, and the nearer it gets to polling day, the more desperate it has got."

Zac Goldsmith has a visible dislike for his Labour rival

Over the past few months, I've spent many evenings watching Goldsmith and Khan debate each other at hustings around the capital. Whereas at first Goldsmith seemed subdued and reluctant to attack his rival, he has since become increasingly aggressive in his attempts to target Khan. Watching the two men together now, Goldsmith's dislike for the man he describes as the most partisan and cynical politician in Britain is obvious and visceral. I ask Khan whether off-stage relations are still civil.

"It's peaks and troughs. When the contest first began, we got on really well. We shook hands, we talked before we went into the hustings and stuff. But there's been periods where he's not wanted to talk to me. That's his choice. I don't take it personally in a sense that in a democracy you should be challenged by the media, you should be asked tough questions by the public, your opponent should look for holes in your case, right.  But their campaign has not been about that and I think it's for them to reflect [on that]."


Video by Jem Collins

Goldsmith insists that his campaign against Khan has not been designed to exploit anti-Muslim feeling among Londoners. Yet few watching his attempts to draw an association in voters' minds between the Labour candidate and Muslim extremists can be under much doubt about his intention. Several Muslim Conservative politicians have spoken out against it, including the former Tory chair Baroness Warsi, who tweeted: "If Sadiq Khan isn't an acceptable enough Muslim to stand for London mayor, which Muslim is?" Life-long Conservative-voting commentator Peter Oborne has described it as "the most repulsive I have ever seen as a political reporter".

Yet allegations of racist dog-whistling have not stayed Goldsmith's hand. Over the weekend, an article by Goldsmith about Khan appeared in the Mail on Sunday with the headline: "On Thursday, are we really going to hand the world's greatest city to a Labour party that thinks terrorists are its friends?". It was accompanied by a picture of the London bus blown up by Islamic terrorists in 2005. Goldsmith's campaign have denied any role in the photo choice but refused to criticise it when asked several times by Politics.co.uk. Asked about it again on LBC yesterday, Goldsmith replied that he thought the photo was "inappropriate," but stood by his campaign's attacks on Khan.

Many of those attacks have been based on Khan's work as a human rights lawyer, when he represented (in his own words) some "pretty unsavoury characters". Khan still defends his decision to do so.

"One of the things I find frustrating about some of the criticisms of me as a human rights lawyer is that, in a civilised mature democracy, you've got separation of powers – you've got the executive, you've got the judiciary, you've got the legislature – and it's right that the executive are held to account by the judiciary and that's why you've got human rights lawyers. Human rights aren't just for middle class articulate journalists, they're for everyone, so for someone not to understand that you can be a human rights lawyer and not necessarily agree with the views of your client, I'm surprised that a senior Conservative politician doesn't get that."

"When I was growing up it wasn't uncommon to be called the P-word"

Khan has been reluctant to accuse Goldsmith of racism personally, leaving it to the likes of Yvette Cooper and others to attack him. However, I wonder how his own personal experience of racism has shaped him.

"I was born and raised in London," he says. “My parents came here as immigrants in the sixties and my dad would tell me stories of when he first came here by himself and my mum was still in Pakistan.

"He was in a bedsit in Earls Court and there would often be signs there saying: 'No blacks, no Irish, no dogs' and by blacks they meant anyone who wasn't white."

"When I was growing up it wasn't uncommon to be called the P-word and end up in fights and scuffles. One of the reasons why we got into boxing, our family, was self-defence really… but it wasn't uncommon when I first started going to watch football matches that I was racially abused."

These experiences continued into his adult life.

"As a lawyer, there would often be prejudgements made if you were a smart man in a suit," he says. "You are clearly the defendant, or a client or the court clerk, rather than the lawyer.

"Obviously part and parcel of growing up in the eighties and being a professional in the nineties, if you are a minority, is that you experience this stuff. Whether it's being stopped and searched or whether it's being asked questions that you otherwise wouldn't be asked."

Khan insists that times have changed. "I live in the same area I was born and raised in, we live about ten minutes away now,” he says. "My daughters, who are aged 16 and 14, I asked them recently and they said they've never been called the P-word. They've never been racially abused. Like me, they've got friends from all different backgrounds. And that shows the progress made over the last twenty, thirty years.

Is Sadiq Khan the radical politician Goldsmith accuses him of being?

Part of the reason why identity politics has dominated the campaign, is that when it comes to policy, there is little to choose between the two men.

On the issue that most Londoners say they're concerned about – housing – the two men sound very similar. Both say they will 'tackle the housing crisis' yet neither will tie themselves to a specific number of new houses to be built each year. Both suggest that London needs at least 50,000 new homes a year, yet only a fraction of that number have been built in the past year by the current mayor. Neither seem confident of their ability to radically turn things around.

"The experts say we should be building 50,000 homes a year. I'd love to do so. What's more important is the types of homes we build," he tells me.

Yet the same experts who suggest London should be building tens of thousands of new homes a year also suggest that this will inevitably mean building on the green belt. In the past, Khan has batted this point away by suggesting that Transport for London owns the equivalent of "16 Hyde Parks", which could be built on. What he doesn't always go on to say is that 90% of that land is occupied by tracks and stations which can never be built upon, meaning the mayor's real ability to radically increase housing supply is much more limited.

Meanwhile, his rival Goldsmith has instead promised to demolish and rebuild London's council estates. This would be hugely controversial and take many years to complete. Given the urgency of the housing crisis facing London, I ask Khan whether it's inevitable that whoever becomes mayor will eventually have to build out into the green belt.

"No," he insists. "Look around London. There are some good quality high density homes in places like Kensington and Chelsea. The issue is design. We could double the density of homes and still be less dense than Paris.

"The green belt is the lungs of our country. In a city like London, where almost 10,000 people die every year because of air pollution, where children's lungs are under-developed, our air is in breach of the air quality directive, the idea of having less green space rather than more doesn't make sense to me."

On this issue, as on others, Khan is reluctant to risk controversy. Contrary to Goldsmith's portrayal of him as a "radical" politician, Khan has been highly cautious and almost small-c conservative in his policies. Unlike Ken Livingstone, who was elected on radical policies like the congestion charge, Khan has stuck carefully to a largely uncontroversial set of proposals. Like a boxer trying to win on points rather than force a knockout, this strategy has underwhelmed some observers. It has also disappointed some of his supporters, who had hoped he would be much bolder.

Leading transport commentator and Labour supporter Christian Wolmar has been on the campaign trail for Khan ever since losing his own bid to be the party's mayoral nominee. Yet he tells me he has been "disappointed" with Khan's agenda, particularly on transport.

"I think they're trying to play it safe to avoid being criticised," he says. "Nobody in this debate has addressed the fundamental issue, which is that we really need to get people out of their cars and unless we do that we're not going to achieve the things we need to. It's disappointing that more hasn't been made of that."

Despite this, he's hopeful that Khan will be bolder in office.

"I think he will be a innovative and interesting mayor but he's got to hit the ground running and be brave."

London is now regularly hit by smog episodes

Khan's caution has made it difficult to work out exactly where he stands on some of the biggest issues facing London.

London's toxic air pollution is one major issue that has been little-discussed during this campaign. Scientists say that levels of noxious gases in the city's air are currently contributing to thousands of deaths a year. In the past Khan has promised he will tackle this by being "the greenest mayor ever" yet he has refused to rule out building Boris Johnson's planned new road links in East London across the Thames. I ask him how he can square the two.

"I've never used the words road crossings throughout this entire campaign," he insists. "The word is river crossings."

So will he build new roads in East London? I try again to draw him out.

"Let me tell you the challenge we've got. We're a city whose population is 8.6 million. We're going to nine million in 2020, 10 million in 2030. The population is rising. We need to think about crossings in the east of London. If you stand on Tower bridge and look west there are 18 crossings, but east there's only one… You're right to challenge me that they've got to respect our environment. They've got to respect air quality. They've got to respect the area.

"So that's why I'm against the current plans…" he quickly corrects himself: "Why I've got real concerns about the current plans for the Silvertown Tunnel, because it's just for cars and lorries. By the way people in south and east will pay for that in tolls."

I try again. Would he rule out building Silvertown?

"I'm not happy with the current plans," he say, before adding: "I don't think you can look at the east of London with just one crossing."

Despite equivocating on this, he's much clearer in his support for new public transport crossings.

"I love the bridge in Copenhagen. I forget the name of it – the swing-back bridge. Actually Caroline Pidgeon [the Liberal Democrat candidate], to give her credit, has been talking for years about the Rotherhithe – Canary Wharf [cycle pedestrian] bridge, which I've pinched. It's a great idea. It's really exciting if we can do that in London. But that's how we should be thinking about lots of different crossings in east London so you don't have all your eggs in one basket.

"That's what leads to people using their cars and lorries and air quality getting worse. So we need to have a look at all the part of London. We need to make it safe and easy to cycle. We need to think about the DLR extension and the Bakerloo extension extending south."

Yet Khan's plans to freeze fares in cash terms could prevent some of these projects going ahead. Khan claims the freeze would cost Transport for London £450 million over four years and could be funded by efficiencies, whereas TfL say the real cost could be closer to £1.9 billion over five years. Doing so would require cutbacks on a scale which City Hall has never seen before plus council tax hikes. Khan's rival, the Green party candidate Sian Berry, describes it as a "George Osborne austerity policy". Yet Khan insists the cuts could be easily accommodated by TfL.

"TfL thinks the only way to raise revenue is to raise fares. They're not being innovative. I don't know a single business or public authority that has not made changes over the past eight years and got rid of inefficiencies and got rid of waste."

He suggests that TfL are wasting hundreds of millions of pounds every year.

"Because of fare evasion last year, TfL lost £61 million. If you go to Bromley-by-Bow the gates are always open. What business would lose £61 million by fraud? It's ridiculous. Because of wastage from this current setup, £900 million pound was lost on the tube contract with Bombardier. We've got two separate engineering departments: one for the underground and one for the surface. What other business would duplicate that kind of expenditure?"

He claims TfL can turn itself into an internationally competitive organisation.

"Think about buses in London: We've got 18 different franchises running our buses, none of them TfL, by the way. Forty per cent of those companies are owned by the governments of France and Germany and Holland. They're savvy enough to have companies bidding for contracts overseas to reduce the fares there. Why aren't we bidding for contracts? Think about the contactless card. Why aren't we selling some of that technology, the knowledge, the information, to other parts of the world? That's the sort of TfL I want to see."

Khan is clearly happy talking about the intricacies of bus franchise contracts. Yet this Thursday's election is unlikely to be won or lost on such matters. Instead, voters will likely choose based on instinctive judgements about the candidates and their parties. 

Is Sadiq Khan a calculating 'machine politician'?

One of those instinctive perceptions of Khan is that he is a "flip-flopper" and a political opportunist.

The main case for the prosecution is that he nominated Jeremy Corbyn for the leadership, only to quickly distance himself from him once he won his own nomination. He has also reversed his position on issues like Heathrow expansion and the mansion tax. Khan's opponents say this the sign of a "machine politician" who will do whatever it takes to acquire power.

"What's really important is that we have lost two elections in a row in the Labour party – 29% in 2010 and 30% in 2015. I thought it was wrong for the Westminster elite – that's what we MPs in Parliament are as far as the membership are concerned – to have deprived the membership of the full slate of candidates. I was very clear on the day that I nominated Jeremy that I had no intention of voting for him. So if I was being cynical, as was being alleged, then I'd have supported him in the leadership and voted for him.

"When asked if I’d serve in Jeremy's Cabinet if I wasn't to be the Labour candidate, I've said no, because we've got a different analysis of things, we come from different wings of the party, we've got a different view on things and I've been quite clear that I will be my own man in City Hall."

Last week Khan and Goldsmith appeared at the Copper Box Arena in the Olympic park for an event organised by the London Citizens network of religious and communitiy organisations. Goldsmith ambled onto stage to polite applause, whereas Khan leapt onto the stage to a roar from the young, mostly left-leaning audience. His booming delivery stood in stark contrast to the much more reticent Tory candidate. While he is unlikely to ever be able to compete in a battle of personalities with the current Conservative mayor, Khan at least looks like a man who is willing to fight for the job.

Many of those who have watched this race closely have been impressed with his determination to do whatever it takes to win. When the row over Livingstone's comments about Jews and Hitler broke shortly after my interview with him, Khan reacted decisively to call for the former mayor to be suspended. Khan's willingness to ditch the man who had previosuly endorsed him was a sign of the kind of ruthlessness which has made him both admirers and enemies within his own party.

Khan has been heavily tested during this campaign and for the most part he has stood up to scrutiny. His behaviour under fire has been in stark contrast to that of Livingstone, whose often erratic performance in the last two mayoral elections (and in recent days) only served to play into his opponents' hands. Yet despite everything, Khan is reluctant to criticise his opponents.

"I've got family who live in Pakistan. In Pakistan's history I think there has only been one smooth transition after a democratic election. More than half their life has been lived under military rule. You speak to my cousins and family in Pakistan, they would die for a democracy where politicians are actually tested, so I think it's a great thing that we have got a free press and I think it's a great thing that I can't tell you what to write, however much I wish I could. That's what living in a democracy is all about."

When Khan first announced his decision to run for London mayor, few believed he could manage it. Even on the day of Labour's mayoral announcement, most commentators assumed that Labour's Tessa Jowell would scoop the nomination, yet Khan ended up winning by a landslide. Once selected, senior London Labour politicians told me that Khan had "no chance" of winning against Goldsmith. Yet, the polls and bookies now suggest he is the overwhelming favourite to become the next mayor of London this week.

The polls may all be wrong and his dream may yet be scuppered, but whatever happens, it's clear that he has been repeatedly underrated as a competitive politician. On Friday evening we'll find out whether he has been underestimated once again.