Sadiq Khan has discredited Labour by appearing alongside David Cameron at an EU referendum campaign event, the party’s shadow Chancellor has reportedly claimed.

It comes after the newly-elected mayor of London appeared alongside the Prime Minister in front of students in south-west London and said he would work closely with the Tory government “where it is in Londoners’ interests”.

But, according to Politics Home, John McDonnell, who was speaking at a Labour In For Britain event on Monday evening, was asked by a member of the audience whether – like the mayor of London – the party should put aside its differences and work with the Tories to keep Britain in the EU.

Mr McDonnell replied: "The Europe that the Tories want is not our Europe. Cameron went to negotiate away workers' rights in advance of this referendum. If he could have done it, he would have done.

"If Cameron and his crew are still in power after this referendum they will continue dismantling our welfare state. They will continue to cut benefits, undermine wages and cut public service jobs. This will go on.

"Sharing a platform with them discredits us. It demotivates the very people we are trying to mobilise."

Responding to the comments Mr Khan's team told The Independent: "It should come as no surprise that Sadiq is campaigning with the Prime Minister for Britain to remain in the EU, as he made it crystal clear that he would do so throughout the Mayoral election.

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"It is deeply concerning that the polls today suggest that Labour voters are unsure where the Labour Party stands on the referendum. Sadiq won't miss a single opportunity to make it absolutely clear to those voters where Labour stands on the referendum."

Standing next to the Prime Minister on Monday, Mr Khan added: "The reason why London is the greatest city in the world – and it is – we have never taken an isolationist approach, we are open-minded, we are outward-looking, we embrace other cultures and learn from other cultures and ideas as well.”

Mr Cameron publicly shook hands with the mayor and said:"In one generation someone who is a proud Muslim, a proud Brit and a proud Londoner can become mayor of the greatest city on earth," he said as he offered his congratulations.

"That says something about our country.

Sadiq Khan's 5 most significant policies Show all 5 1 /5 Sadiq Khan's 5 most significant policies Sadiq Khan's 5 most significant policies Tackle the housing crisis Khan’s key policy is an ambitious target to make 50 per cent of all new homes being genuinely affordable, and improving conditions for people renting Getty Images Sadiq Khan's 5 most significant policies Freeze transport fares Khan says he will freeze London transport fares for four years and introduce a one-hour bus ‘Hopper’ ticket, paid for by making TfL more efficient and exploring new revenue-raising opportunities. He claims Londoners won’t pay a penny more for their travel in 2020 than they do today Getty Images Sadiq Khan's 5 most significant policies Make London safer Resore neighbourhood policing, tackle gangs and knife crime, and a new plan to tackle the spread of extremism, and a review of the resourcing of our fire service Getty Images Sadiq Khan's 5 most significant policies Restore London's air quality Pedestrianise Oxford Street and prioritise measures to improve London’s air quality Getty Images Sadiq Khan's 5 most significant policies Make cycling and walking safer More segregated cycle routes with a promise to spend money improving dangerous junctions Getty Images

"There are still barriers to opportunity that we have to get rid of. There are still glass ceilings we have got to smash. There is discrimination in our country that we have to fight.

Mr McDonnnell, who is a close friend of Labour leader Jeremy Corbyn, today began a week-long tour of the country with events scheduled in Wolverhampton, Leeds, Leicester and Cardiff.

Speaking on ITV’s Peston on Sunday, Mr Khan added: “Is it in London's interest for me to hold grudges? Is it in London's interests for the mayor of London to be at permanent war with the Conservative prime minister?”

“We're never going to be best friends, but what is important is that the mayor of London argues the case for London and for Londoners to remain in the European Union. This debate is far more important than David Cameron or me. It's about our city's future and country's future".