The London mayor and British prime minister jointly launched a Britain Stronger in Europe battle bus, while Labour leader Jeremy Corbyn refused to campaign with David Cameron. Khan explained why he decide to campaign with the Conservative PM.

"There are many things on which the prime minister and I will disagree. But what's really important is when it's in Londoners' interests for the mayor and the government to work closely together, we will work closely together," he said from the rally in Roehampton in south-west London on Monday (30 May).

By remaining in the EU there would be more measures to protect workers' as well as women's rights and "finally breaking the glass ceiling" Khan claimed. He called for young people to register to vote and "get involved" according to a BBC report.

Prime Minister Cameron took to the podium after Khan, congratulating him on becoming the London Mayor. He described the 45-year-old former MP for Tooting as "someone who is a proud Muslim, a proud Brit and a proud Londoner can become mayor of the greatest city on Earth. That says something about our country".

Cameron agreed that there were many differences between the two politicians, pointing out that he was the son of a stockbroker while Khan was the son of a bus driver. But the prime minister acknowledged they were part of an "incredibly broad campaign" in favour of EU membership. He added: "It's about our city's future and country's future."

The PM highlighted the campaign as an "extraordinary coalition – Labour, Liberal, Conservative, Green, business, trade union, NGO – all together knowing this is the right answer."

He denied claims of a "massive establishment conspiracy" if Britain votes to leave the EU. Cameron said: "It would be a pretty exquisite conspiracy that could bring together the Labour mayor, son of a bus driver and the Tory son of a stockbroker Prime Minister. Sadiq and I say it for this reason: because we love our country, we want our country to be the best we possibly can, to be the strongest, to be the greatest."

The two men disclosed a "five-point guarantee card" stating what voters stand to gain if they are in favour of the Remain campaign. The points include "full access" to the EU single market; protection of workers' rights, and the Schengen passport-free area.

Labour leader Jeremy Corbyn had earlier ruled out sharing a platform with the Tory leader. Appearing on ITV's Peston on Sunday, Corbyn said: "I don't think it would work. Do you think it'd work? It'd be good television but it's not going to happen, OK?"

An animated history of the European UnionIBTimes UK