How Zac Goldsmith could still beat Sadiq Khan to become Mayor of London

With a series of polls giving Labour's Sadiq Khan strong, double-digit leads over Conservative rival Zac Goldsmith, it's understandable that many believe a Tory victory tomorrow is now impossible short of a second bad night for the UK polling industry.

I think this assumption is partly being fuelled by some media outlets and hopeful Labour activists fixating on Sadiq's headline leads and so inadvertently misunderstanding or mischaracterising the challenge ahead for Zac.

Let's have a look at today's Comres poll for ITV and LBC - after second preference votes are counted this puts Sadiq on 56% versus 44% for Zac.

At face value the Tory hopeful will find it all-but impossible to close 12 points behind his Labour rival and in a First-Past-the-Post Election that sort of deficit would almost certainly spell electoral doom.

But the two-round voting system used in the London mayoral election means his challenge is potentially more manageable.

After Londoners have voted for their preferred choice of the 12 mayoral runners, all but the top two (almost certainly Sadiq and Zac) will drop out and any valid second preference votes cast for them by supporters of the losing 10 will then be added to their total.

At this point victory is achieved simply by taking 50.01% of the second-round vote.

So despite the poll's headline numbers, Goldsmith doesn't have to pick up 13 points to overtake Khan's lead he just needs to add an extra 6.01% to the 44% Comres suggests he'll get in the final run-off.

If the polls are even a couple of percent out, and of course they can be out in either direction, then the actual gap Goldsmith needs to bridge could be even narrower.

When Goldsmith tells gatherings of party activists that "this election will come down to the wire" and that every leaflet they deliver could mean the difference between victory and defeat, he's not just going through the motions - his campaign really does believe that they're in with a chance of victory.

They've even sought to make a virtue of the polling by featuring an ITV headline reporting Khan's poll lead on their most recent flyer in order to galvanise their supporters into campaigning and voting.

There are a number of other factors that could upset expectations - if Labour's past warnings about their voters disproportionally falling off the electoral roll following changes to registration are more than scaremongering, it's possible that some would-be Khan backers won't actually be allowed to vote.

And there are those of us who stubbornly believe that with real-world turnout likely to be far lower the pollsters' predictions of 50% to 62%, and with turnout varying considerably across London, the pollsters could just be calling this wrong.

But even though I'm always sceptical of opinion polls' predictions of election outcomes, I do think they're an excellent way of gauging voters' perceptions of campaigns and the issues, and today's Comres has some interesting findings.

The past few weeks have seen a disappointing shift away from policy discussion to coverage of Tory attempts to link Sadiq Khan with the "extremist" views of people who spoke at events he attended and very loud and angry Labour accusations of Tory "racism".

And yet the poll suggests voters are largely unexcited by either sets of accusations.

It's true that Goldsmith and the Tories (14%) are more likely to be seen as "racist" than Khan and Labour (8%), but that relatively low number suggests Labour hasn't even convinced the majority of their own supporters on this point.

Meanwhile Khan is more likely to be seen as "slippery" (28%) than he is "dangerous" (21%) or "extreme" (20%) despite all the efforts to link him to unsavoury types and their views.

This isn't a huge surprise - voters are used to politicians making rude, insulting and outlandish claims about one another and, while online activists can't wait to vent their outrage, simply factor it in as part of the process.

Comments made at the last Mayoral election led the late RMT union leader Bob Crow to try suing Boris Johnson for defamation, but chucking the case out, Mr Justice Tugendhat said:

"In the context of an election, statements by one candidate about another candidate, or about a person associated with another candidate, are not capable of being understood as anything other than partisan."

Today's poll suggests that's a pretty fair assessment of how voters see things and that they correct accordingly.

Martin Hoscik is a political journalist and commentator who has covered the capital's mayoralty since its inception in 2000 and is the editor of MayorWatch.co.uk