Labour has been embroiled in a fresh controversy after it emerged that its mayoral candidate, Sadiq Khan, used a slur against fellow Muslims while appearing on Iranian television in 2009.

During an interview with Iranian state-backed TV channel Press TV, Mr Khan used the term “Uncle Tom” to describe certain members of the Muslim community - a derogative term for a member of an oppressed minority who supposedly choses to be subservient to their oppressors.

It comes as the chief rabbi, Ephraim Mirvis, said Labour had a "severe" problem with anti-Semitism that would get worse if the party's inquiry into the issue was used as "sticking plaster" to placate voters.

He wrote: "If this inquiry turns out to be no more than a sticking plaster, designed to placate and diffuse until after the elections this week, the problem will surely get worse and not better.

"Jeremy Corbyn has stated that his party 'will not tolerate anti-Semitism in any form', and I very much hope that this inquiry will deliver on that pledge and be followed by decisive action.

Mayor of London 2016 - the candidates at a glance Show all 7 1 /7 Mayor of London 2016 - the candidates at a glance Mayor of London 2016 - the candidates at a glance Sadiq Khan - Labour The MP for Tooting, Sadiq Khan says the mayoral election will be a 'referendum on the Tory housing crisis'. He has also pledged to freeze fares until 2020. Son of a bus driver, and doesn't let anyone forget it. His Conservative opponent has made claims about people who he has previously associated with - but attacks so far have failed to stick Mayor of London 2016 - the candidates at a glance Zac Goldsmith - Conservative The MP for Richmond, Zac Goldsmith is a longstanding campaigner against the expansion of Heathrow airport. Despite his environment credentials - he once edited The Ecologist magazine - the Tory candidate has said he would 'rip out' Boris Johnson's cycle lanes if they don't work. A very wealthy man, his campaign has been dogged by accusations of racism against Sadiq Khan Mayor of London 2016 - the candidates at a glance Sian Berry - Green Party A councillor in the London Borough of Camden, Sian Berry is campaigning on improving homes for renters, cleaning up London's air pollution, and flattening fare zones to help Londoners. She previously ran as the party's mayoral candidate in 2008. In 2012, the Green Party came in third place Mayor of London 2016 - the candidates at a glance Caroline Pidgeon - Liberal Democrat A Liberal Democrat London Assembly member for eight years, Caroline Pidgeon has a strong record on the Assembly's transport committee standing up for commuters and cyclists alike. She wants to set up a £2 billion housing investment fund and make all the capital's buses zero emission Mayor of London 2016 - the candidates at a glance Peter Whittle - UKIP UKIP hasn't fared so well in London in previous elections, but is hoping for a breakthrough this time. Peter Whittle has been UKIP's culture spokesperson for two years. He tends to focus on the impact of immigration on London's housing crisis Mayor of London 2016 - the candidates at a glance George Galloway - RESPECT George Galloway has made a habit of defying the odds and pulling off stunning victories when standing for Parliament. His campaign - based on the slogan 'a London for all' has so far failed to make headway in the polls - has his luck run out? Mayor of London 2016 - the candidates at a glance Sophie Walker - Women's Equality Party A journalist, Sophie Walker is campaigning for the little-known Women's Equality Party. She is pledging to make 'equality and diversity the fuel that drives our nation's capital' with measures to increase women's representation in enterprise, more affordable homes and flexible childcare

The offensive term used by Mr Khan derives from a 1852 anti-slavery called Uncle Tom’s Cabin by abolition campaigner Harriet Beecher Stowe which tells the story of a black slave called Uncle Tom who is depicted as a long suffering, Christ-like figure who is eventually killed by his master.

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The author initially wanted him to be viewed as a heroic character, but it is widely considered to be a pejorative term today.

In the footage, he describes his work as minister for community cohesion in the Labour government and said he was talking to all members of the community whether he agreed with them or not.

He said: “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.”

Sadiq Khan talking to a Press TV reporter in 2009 (Press TV/YouTube)

It comes as Mr Khan has attacked his rival for London Mayor, Conservative candidate Zac Goldsmith, for attempting to smear him by accusing him of being an extremist.

Mr Goldsmith insisted his campaign was not racist and that he was simply raising legitimate concerns about Mr Khan’s priorities and who he had shared a platform with in the past.

He said Mr Khan had given "platform, oxygen and cover to extremists".

In an interview with the London Evening Standard last month, he said: “I think he is playing with fire. The questions are genuine, they are serious. They are about his willingness to share platforms with people who want to ‘drown every Israeli Jew in the sea’”.

Last week, Mr Khan condemned the use of the Uncle Tom phrase when he was asked about the anti-Semitism row which had exploded within the party after Ken Livingstone made comments about Hitler and Zionism.

Asked on LBC whether he considered the term to be racist, he said: “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.”

Mr Khan's team said he "regrets" using the phrase, used against black people to suggest they are subservient to whites.

A 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."