Labour's candidate for London Mayor has issued a grovelling apology after it emerged that he had described moderate Muslim groups as 'Uncle Toms'.

Sadiq Khan said he regretted using the term, which is notorious racial slur used against black people to suggest that they are subservient to whites.

But he also insisted he would 'respect' everyone in the capital if he was elected, and lashed out at tactics employed by Tory rival Zac Goldsmith during the battle.

Labour candidate for London Mayor Sadiq Khan out on the campaign trail on Canary Wharf today

The incendiary claim surfaced in an interview with Iranian-backed Press TV from 2009, when Mr Khan was 'minister for community cohesion', in charge of Government efforts to stamp out extremism.

The revelation is a major blow for Mr Khan, who has faced a string of claims about his past dealings with Muslim extremists during the bitter campaign to succeed Boris Johnson.

Sadiq Khan was branded unfit to be London Mayor after it emerged that he had described moderate Muslim groups as 'Uncle Toms' – a notorious racial slur used against black people to suggest that they are subservient to whites

Mr Khan has dismissed Tory attacks as baseless 'smears', and insisted that he was a moderate Muslim.

The Tooting MP himself condemned the use of the Uncle Tom term in recent days while attacking former London Mayor Ken Livingstone for his offensive claim that Hitler was a Zionist.

Asked on LBC Radio at the weekend whether he considered terms such as 'Zio and Uncle Tom' to be racist, he replied: 'They are racist, they should not be used. The harsh truth is this – the comments from Ken Livingstone were appalling and disgusting and should have no place in our party.'

Challenged about 2009 the comments in interviews today, Mr Khan said: 'It is (a racial slur) and I regret using that phrase.

'The context was me trying to encourage everyone to get involved in government consultations.'

He told ITV News London. 'I was a minister at the time. It was wrong and I regret it.'

Speaking on LBC he said: 'I regret using the phrase and I am sorry.

'The point I was trying to make was that I wanted to talk to anyone.'

Mr Khan suggested he himself would have been a target for the slur, pointing out that there were protests outside his local mosque when he first stood for parliament.

He said he had been 'disappointed' by Mr Goldsmith's tactics during the battle, which have included repeated claims about his links to extremists. 'I thought he was his own man,' Mr Khan said.

Tory MPs said the latest revelations proved Mr Khan was unfit to be mayor of one of the world's most multicultural cities.

Paul Scully, MP for Sutton and Cheam, said: 'Once again, Sadiq Khan has shown he doesn't have the judgment to be Mayor of London.

The incendiary claim emerged in a 2009 interview with Iranian-backed Press TV, when Mr Khan was 'minister for community cohesion', in charge of Government efforts to stamp out extremism

The revelation is a major blow for Mr Khan, who has faced a string of claims about his past dealings with Muslim extremists during the bitter campaign to succeed Boris Johnson

'He's deeply hypocritical on race issue when it suits his political purpose. Labour must show they won't put up with attitudes like this in the party.'

Fellow Tory Andrew Bridgen said: 'It would appear that Sadiq Khan is being hoisted by his own petard.

'He says one thing as a government minister and another thing when seeking election to one of the highest offices of the land as Mayor of London.

'It is clear that the London electorate must ask questions about whether this man is fit to be mayor of the finest city in the world.'

Mr Khan, pictured unveiling a campaign poster today, is hot favourite to win the battle to succeed Boris Johnson as mayor

The row came as Labour struggled to close the anti-semitism row that has engulfed the party in the run-up to tomorrow's local elections.

In other developments:

The Chief Rabbi has urged Jeremy Corbyn and his allies to stop denying there is a problem with anti-Semitism and blaming political opponents for whipping up the row.

The Commons home affairs committee said it would summon Mr Livingstone to grill him on his controversial views in Parliament.

Suspended Labour MP Naz Shah resigned from a Commons inquiry into anti-semitism after it emerged last week she had once called for Israel to be 'relocated' to the US.

A spokesman for the militant Palestinian group Hamas was reported to have praised Mr Corbyn for his willingness to engage with it, saying his stance was a 'painful hit that the Zionist enemy received'. The group later denied it had offered Mr Corbyn its support.

SLUR THAT STARTED IN A NOVEL The phrase ‘Uncle Tom’ has become one of the most controversial racial insults in the US. It derives from Harriet Beecher Stowe’s classic 1852 anti-slavery novel Uncle Tom’s Cabin. The character Uncle Tom is portrayed as a martyr as he is killed by a cruel master after he refuses to divulge the whereabouts of two women who escaped slavery. But his portrayal has long been divisive, with black rights activists arguing he was too subservient to his white masters. As far back as 1919, the radical preacher Reverend George Alexander McGuire said: ‘The Uncle Tom n***** has got to go, and his place must be taken by the new leader of the Negro race... not a black man with a white heart, but a black man with a black heart.’ It is now used as an insult aimed at black people to suggest they are too eager to please whites. Advertisement

Mr Khan is hot favourite to win the mayoral race against Tory Zac Goldsmith tomorrow, potentially delivering a sliver of cheer for the party on what otherwise looks set to be a grim night of results.

A ComRes poll for LBC radio and ITV London has given him a 45 per cent to 36 per cent advantage over his rival on first preferences.

It forecast Mr Khan will win by 56 per cent to 44 per cent in the final run-off.

The Tooting MP has used his campaign to distance himself from Mr Corbyn's hard-Left politics. Yesterday he urged the Labour leader to 'get a grip' on the anti-semitism crisis as he tried to build bridges with the Jewish community.

But the fresh revelations will raise fresh questions about his own stance.

Boris Johnson last night warned Mr Khan would turn the capital into a 'Petri dish' for Mr Corbyn's policies.

Speaking at a rally for Mr Goldsmith, Mr Johnson said he had captured City Hall from the 'Livingstonians and Corbynistas'.

He added: 'Sadiq Khan has emerged from that strain of political thinking.

'Do we want these people back running City Hall? Do we want our city to be the Petri dish for Corbynism?'

In the 2009 interview with Press TV Mr Khan was asked why the Government's counter-extremism strategy focused on working with moderate Muslim groups like the respect Quilliam Foundation.

He responded: 'I wish we only spoke to people who agree with us. I can tell you that I've spent the last months in this job speaking to all sorts of people. Not just leaders, not just organisations but ordinary rank and file citizens of Muslim faith and that's what good government is about, it's about engaging with all stakeholders. You can talk about articles in the newspapers about what an organisation might get but the point is you can't just pick and choose who you speak to, you can't just speak to Uncle Toms.'

Mr Khan is favourite to win the mayoral race against Tory Zac Goldsmith tomorrow, potentially delivering a sliver of cheer for the party on what otherwise looks set to be a dismal night of results

In a wide-ranging interview, Mr Khan also appeared to suggest he supports controversial boycotts of Israeli products.

Asked about Muslim anger over Western policy in the Middle East, he said: 'You know, there's nothing wrong, and I encourage people to protest, to demonstrate, to complain, to write into newspapers and TV, to, if you want to boycott certain goods, boycott certain goods - all lawful means open in a democratic society.'

You can talk about articles in the newspapers about what an organisation might get but the point is you can't just pick and choose who you speak to, you can't just speak to Uncle Toms

In a statement last night, a spokesman for Mr Khan acknowledged that the use of the phrase 'Uncle Tom' has been a mistake.

The spokesman said: 'This was a bad choice of phrase and Sadiq regrets using it.

'As Communities Minister at the time, Sadiq was talking about the need to engage with all parts of the community to tackle extremism and radicalisation - as he has pledged to do as Mayor.

'Sadiq does not support boycotts of Israel in this video - he merely says it is 'lawful' - which it is. Sadiq opposes boycotts and sanctions against Israel.

'He also makes it crystal clear that 'you can't use Iraq or Gaza as an excuse' for extremism and terrorism.‎'

The Quilliam Foundation last night declined to comment on Mr Khan's intervention.