Next Thursday, one of two men will be elected mayor of London.

I mean, I don't want to sound like I'm pre-judging this: there are actually 12 candidates in the race. Some of them – such as the Green's Sian Berry, who has treated her campaign as a good opportunity to broaden the debate – are serious. Some of them – celebrity hat fan and cat impersonator George Galloway of Respect; a man claiming to be the exiled Emperor of Jammu and Kashmir – are not.

In practice, though, short of a polling upset that'd put "Dewey Defeats Truman" into some sort of perspective, only two of them actually stand any chance of winning on Thursday. London's next mayor will be either the Conservatives' Zac Goldsmith, or Labour's Sadiq Khan.

I'm a geeky, wonkish guy running a geeky, wonkish website. You can probably imagine what I really want from my mayor. A detailed plan to fix the capital's crippling housing crisis would be good. A plan to fund Crossrail 2, or to turn South London's train network into a proper urban S-Bahn network – those would be nice, too. I'd also like some clues as to how we're going to reduce air pollution, or to make the roads safe for cyclists without bringing traffic to a halt.

But on this score, frankly, both leading candidates have been a massive disappointment.

In the blue corner

Goldsmith's manifesto is full of appealing promises ("I will double the rate of house-building", "I will ramp up Boris's cycling revolution"). A few of these promises are backed up with explanations of how he would achieve them; rather more of them aren't.

More to the point, though, there's no vision connecting them, no sense of how Goldsmith actually thinks London should be. (In interviews, in fact, he's relied so heavily on examples from his own Richmond constituency, that you wonder if he's actually visited the rest of London at all; if not, it would at least explain his bizarre ignorance of the Central line.)

The impression you're left with is that the main reason Goldsmith wants to be mayor is to stop Labour. A Goldsmith mayoralty would be continuity Boris Johnson, only without the occasional flashes of burning personal ambition.

In the red corner

It'd be nice, at this point, to be able to say that Khan was different – that he was offering a compelling and coherent vision for the capital.

He certainly seems to want it more: where Goldsmith seems laid back to the point of narcolepsy, Sadiq seems like a main who'd auction his own kidneys to get the big job at City Hall. He's made more striking policy announcements, too, promising a "London living rent" (in which new affordable homes will be priced at no more than a third of local wages), and a freeze in transport fares.

Both of these policies are exactly the sort of things that should appeal to London's voters. But that is exactly the problem – they promise free goodies for all, with no indication of how we're going to achieve them. (Freezing fares, for example, will leave a worrying hole in Transport for London's budget.) Without that, they look like cynical giveaways, rather than a real plan for London.

What's more, for a man who's made it the centrepice of his campaign, Khan is depressingly weak on housing – or at least, on house building, without which this crisis isn't going anywhere. He's promised to block development on green space, and to ensure estate regeneration only takes place where there's strong support from existing residents. He's hinted he'd oppose towers, too, and said he'd require developers to include more affordable homes in future developments.

Khan, too, has promised 50,000 houses a year, but given all the above, what I can't work out for the life of me is where he expects to put them. (TfL land, yes, but what then?) The housing crisis is fundamentally a land supply crisis, and Khan's plans don't address that – might, in fact, make it worse. It's not clear whether a mayor who enacted these policies would leave London's housing market in a better state than he found it.

So, on the biggest single issue facing London – on the thing that I care about most, and write about most, and bang on about constantly, no matter how inappropriate the social situation (seriously: funerals) – Sadiq Khan is weak, at best.

And yet...

And yet, I'm going to vote for him anyway. Not reluctantly, not in a "needs must" kind of way, but with genuine enthusiasm.

The offensive way in which the Goldsmith campaign has operated has been much discussed. It's implied, repeatedly, that Khan can't be trusted – that he has links to extremists, or will enact policies (no, really) that will steal jewelery from London's other South Asian communities. Again and again, Goldsmith's proxies – the prime minister; the front page of the Evening Standard – have insinuated that there is something not quite right about Khan. Even this morning, the current mayor of London Boris Johnson has claimed there is a "continuum" between Khan's views and the antisemitism that Ken Livingstone was spouting yesterday.

There's a technical term for this kind of messaging: it's "bollocks". Sadiq Khan is about as liberal and moderate a politician as you're likely to find. (He voted for gay marriage, and received death threats for his trouble). He's also been as outspoken in his opposition to antisemitism as anyone in British politics. Yesterday, in an unlikely move, he called for Livingstone – Labour's last mayor of London! – to be thrown out of the party, a week before the mayoral election.

But it's not enough – it's never enough. Goldsmith and his party are implying that Londoners should think twice about voting for Sadiq Khan, and while they don't quite say it out loud, the reasons always seem to link back to the fact he's a Muslim.

On the most visceral level I don't want my city to have a mayor who thinks that's okay. More than that, if Goldsmith's tactics work – in a city as diverse as London, where the polls currently show Khan 20 points ahead – you can be damn sure we haven't see the last of this kind of racially-charged divide and rule strategy. That alone would be a good reason to vote for Khan.

But there's another. And Khan's religion isn't irrelevant: it's very relevant indeed.

There are forces – in far right politics, and in parts of the Islamic world – that want us to think that western civilisation and Islam are inherently in opposition to each other. That to defend one means trying to crush the other.

These are bad people – whatever their religion; whatever their skin colour – and we should do everything we can to defeat them. I can't think of a better way of doing that, of sending the message that Islam and the West are not at war, than by a major Western city electing a liberal Muslim as mayor.

CityMetric is politically neutral. I, however, am not – and this Thursday, I will be voting for Sadiq Khan to be London's next mayor.

I'll give him a hard time about the green belt later.

Jonn Elledge is the editor of CityMetric, and tweets too much.

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