Britain's main opposition Labour party has claimed victory for its candidate Sadiq Khan as mayor of London ahead of the formal announcement of final results.

"Congratulations Sadiq Khan. Can't wait to work with you to create a London that is fair for all!" Labour leader Jeremy Corbyn wrote on Twitter.

Labour's Sadiq Khan has broken the Conservatives' eight-year hold on the London mayoralty, beating Tory challenger Zac Goldsmith.

Mr Goldsmith's campaign, labelled "vile" by Mr Corbyn, struggled to resonate across the capital.

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

"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," said Mr Corbyn.

"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.

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."