TORY in-fighting over Europe has reached a new high after party grandee Lord Heseltine launched a withering attack on Boris Johnson, denigrating his comments during the campaign as “preposterous” and “obscene”.

The Conservative peer and long-time Europhile denounced the leading Brexiteer’s behaviour as irresponsible and reckless, which, he claimed, had seriously thrown into doubt the London MP’s capacity one day to lead his party.

The outspoken blue-on-blue attack came after David Cameron raised Vote Leave ire by claiming the leadership of so-called Islamic State was in favour of Britain leaving the EU while the Brexit camp accused the Prime Minister of a "stitch-up" with big business over its campaigning for an In vote.

In yet another day of rhetorical claim and counter-claim between the two sides, the most potent attack was delivered by Lord Heseltine, the former deputy prime minister.

The 83-year-old peer said he did not want to personalise the campaign but had to respond to the "preposterous, obscene" comments made by Mr Johnson.

“His judgment is going…The strain is beginning to tell,” declared Lord Heseltine.

He accused the former London mayor of a "near racist" attack on US President Barack Obama when he referred to him as "part-Kenyan" and he admitted to being "deeply distressed and disturbed" by Mr Johnson's comments about how Adolf Hitler and the Brussels bloc shared the goal of creating a political superstate.

"My generation remembers what it was like…We know what Hitler was about. It was about the most manic nationalistic aggressive destruction on a scale unprecedented in human history. It was about the persecution of the Jews…The idea that a serious British politician can in any way invoke that memory I find...frankly, I better contain my language.”

The peer also picked up on Mr Johnson’s claim, during campaigning, when he denounced the EU for its “absurd” regulation that prevented bananas being sold in more than bunches of three.

Lord Heseltine noted: “Today we've got some ridiculous story about two to three bananas in a bunch out of Brussels. It's a complete fabrication. I know. My wife and I eat bananas, I've bought bunches of bananas."

Earlier, Mr Cameron came under fire from within Tory ranks over claims he misled parliament following a "stitch-up" with big business over EU referendum campaigning.

Prominent Conservative Outer Jacob Rees-Mogg called for an inquiry into the allegations and warned the PM faced having to resign if they were true.

Mr Johnson also claimed the alleged pact between his colleague and the corporate world over campaigning for Remain in the June 23 vote "stinks to high heaven" and that it was “the biggest stitch-up since the Bayeux tapestry”.

It came after a leaked letter from Rupert Soames, the boss of outsourcing company Serco, to the Tory leader revealed how he was looking at how to "mobilise corporates" in favour of Remain during the campaign.

Elsewhere, Mr Cameron used a speech in the City of London to claim the Vote Leave campaign was “losing the argument” after it was reported Ukip’s Nigel Farage suggested that if there was a narrow In vote, there would be a campaign for a second referendum.

The PM said: “When people start arguing for a second referendum before you've even had the first one, that clearly demonstrates you are losing the argument."

He added: "You can't have neverendums; you have referendums."

Also at the World Economic Forum event, Mr Cameron suggested so-called Islamic State’s leader Abu Bakr al-Baghdadi would be happy if the UK voted to leave the EU, which prompted a forceful response from Tom Harris, the director of Scottish Vote Leave, who said: "What a load of rubbish. David Cameron continues with Project Fear in an attempt to scare Scots into voting to stay in the EU."