London Sadiq Khan, a Muslim lawmaker from Britain's opposition Labour Party, is the strong favourite to win London's mayoral election on Thursday after a bitter contest marked by religious tensions and accusations of racism.

Polls show Mr Khan, the son of a bus driver, is as much as 20 percentage points ahead of rival Conservative Zac Goldsmith in the race to run one of the world's top financial centres. If he wins, he will succeed current Conservative mayor Boris Johnson to become the first Muslim to head a major Western capital.

Strong favourite: Candidate for London Mayor and Muslim lawmaker Sadiq Khan. Credit:Frank Augstein

London's population of 8.6 million is among the most cosmopolitan in the world and it is rare for identity politics to enter British campaigning.

Yet Mr Goldsmith, with the support of Prime Minister David Cameron, has for weeks focused on Mr Khan's faith and past appearances alongside radical Muslim speakers, accusing him of giving "platform, oxygen and cover" to extremists.