London :  (IANS) Conservative ministers and senior backbenchers in the Parliament have threatened a “no confidence vote” if British Prime Minister David Cameron fails to stop the “blue on blue” attacks on fellow Conservatives

Cameron may face a leadership challenge after the “in or out” European Union (EU) referendum unless he tones down his attacks on pro-Brexit London mayor Boris Johnson and other Eurosceptics, Xinhua cited a report in the Sunday Times on Sunday.

Under the Conservative Party’s rules, a vote of no confidence can be called if 15 percent of its members of Parliament (MPs) request such a vote.

“Cameron’s position will be untenable even if he wins the referendum if he carries on like this. There will be no problem getting 50 names,” a senior backbench MP was quoted by the newspaper as saying.

The ruling Conservative Party is now openly split over Britain’s future in the EU, with a number of heavyweight cabinet ministers,  leading conservative politicians and more than 120 MPs joining the “out” campaign.

On Monday, Cameron criticised Johnson, the London mayor who has announced his support for Brexit, by suggesting that the mayor’s decision was simply driven by his own ambition to become the next prime minister.

In a column for the Telegraph newspaper on Monday, Johnson admitted that Cameron “has done his very best” in renegotiating British membership in the EU, but insisted that the only one way to get the change Britain wants is to vote to leave.

“This is a once-in-a-lifetime chance to vote for real change in Britain’s relations with Europe. This is the only opportunity we will ever have to show that we care about self-rule,” he wrote.

“A vote to Remain will be taken in Brussels as a green light for more federalism, and for the erosion of democracy,” he added.

Britain will hold a referendum on whether to remain in the EU on June 23.