Labour's Sadiq Khan appears on course to break the Conservatives' eight-year hold on the London mayoralty, with a live count of votes indicating a clear lead.

The Tooting MP has been the frontrunner in the counting process ahead of Tory challenger Zac Goldsmith, according to first preference votes collated using an electronic system.

An official result is not expected until early evening at City Hall, once first and second choice votes have been counted.

But the early signs suggest Mr Goldsmith's campaign, labelled "vile" by Labour leader Jeremy Corbyn, has struggled to resonate across the capital.

Richmond Park MP Mr Goldsmith and Prime Minister David Cameron sought to link Mr Khan with Muslim "extremists" in the bitter race to succeed Boris Johnson.

A source close to Mr Khan's campaign said they are "optimistic" about the result although they adopted a cautious tone with votes still to be counted.

The Green Party's Sian Berry is also seeking to secure third place in the contest ahead of Caroline Pidgeon of the Liberal Democrats and Ukip's Peter Whittle.

Former MP and Respect candidate George Galloway is trailing Sophie Walker of the Women's Equality Party in the live count.

Speaking in Sheffield, Mr Corbyn told the Press Association: "This vile campaign run by the Tories, the way they've tried to smear Sadiq Khan, the methods they've used and the language they've used, has had a very big effect in exactly the way they didn't want.

"So many people are just revolted by what was said about Sadiq yesterday they came out and voted for us."

Senior Conservative politician Andrew Boff, a London Assembly member, also criticised Mr Goldsmith's mayoral campaign for trying to link Mr Khan to Islamist extremism.

He said the team was wrong to equate people of conservative religious views with extremists.

Speaking at the ExCeL centre in east London, where counting for the London mayoral elections was taking place, Mr Boff said: "I was supportive of the whole campaign apart from one element and that one was where it seemed to attribute radical tendencies to people of orthodox religious views.

"I think that is a complete misunderstanding of the patchwork of faiths there are in London, and has the potential to alienate people and say that people who do have orthodox religious views, conservative religious views, are for some reason not welcome and won't be listened to."

Mr Khan is the bookmakers' favourite to win, with a source in Mr Khan's camp saying: "So far as we can tell, things have gone pretty much as we expected.

"Nothing has happened to move our market one way or the other.

"We are optimistic but simply do not believe the big leads we have been getting in the opinion polls."

Labour is still scarred by the shock of the general election defeat, which followed opinion polls putting the party neck and neck with the Tories, and the source said Mr Khan's camp was "massively cautious" as a result.

Outgoing mayor Mr Johnson thanked the capital for his eight years in office as he sent his final messages from the official London Mayor Twitter account.

He tweeted: "It's time to sign off from City Hall - it's been the most amazing privilege to be your mayor."