Boris Johnson has tried to link Labour’s Sadiq Khan to alleged antisemitic comments by Ken Livingstone – despite Mr Khan having branded them as “inexcusable”.

Labour was engulfed in a row over antisemitism this week after it emerged that one of its MPs, Naz Shah, had endorsed a plan to relocate Israel to North America.

Mr Livingstone took to the airwaves on Thursday to defend Ms Shah’s action but found himself also suspended after making a historical reference to Adolf Hitler in a discussion about Israel.

Mr Khan was the first high-profile Labour figure to call for Mr Livingstone to be suspended.

“Ken Livingstone's comments are appalling and inexcusable. There must be no place for this in our Party,” the Labour candidate had tweeted around an hour after the controversial interview aired on BBC London.

However Mr Johnson, the outgoing Mayor of London, has tried to leverage the row over Mr Livingstone into the Conservative mayoral campaign.

He told LBC Radio on Thursday afternoon there was an “ideological continuum” between the two politicians, despite Mr Khan’s loud criticism of Mr Livingstone.

“There’s plainly some sort of virus of anti-Semitism within the Labour party that needs to be addressed,” he said.

Boris Johnson accused Mr Khan of having an 'ideological continuum' with Mr Livingstone (PA)

“It seems to me there’s an ideological continuum between the views of Ken Livingstone about Israel and the position of Jeremy Corbyn and indeed the views of their candidate for London Mayor Sadiq Khan.”

The Tories’ campaign to elect Zac Goldsmith as Mayor of London has been forced to deny suggestions that it is running a “racist” operation.

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

It has previously described Mr Khan, who is a Muslim, as “radical”, and has sought to highlight instances where he had met with “extremist” figures.

Critics have suggested the core strategy of Mr Goldsmith’s campaign is to draw attention to Mr Khan’s faith.

Mr Johnson appeared to call into question Mr Khan’s sincerity over his condemnation of Mr Livingstone.

John Mann MP call Ken Livingstone MP a 'Nazi apologist'

“I think it’s very prudent of the Labour party candidate to do that – although I note that Sadiq Khan had previously called upon Ken Livingstone’s services as an adviser and indeed Sadiq Khan had nominated Jeremy Corbyn, as I recall, to be leader of the Labour party,” Mr Johnson added.

The outgoing Mayor himself was criticised last week for suggesting that US president Barack Obama might have an “ancestral” dislike of Britain due to his “party-Kenyan” heritage.