Boris Johnson's 'obscene' EU comments harming his prospects of being Prime Minister, Lord Heseltine warns

'When he starts invoking the memories of Hitler, that has crossed the bounds of domestic debate'

Lord Heseltine was speaking about the loss of 3,500 steel industry jobs (Getty)

Boris Johnson has made “preposterous, obscene” remarks during the EU referendum campaign, which call into question his judgement and suitability for the job of Prime Minister, senior Tory Lord Heseltine has said.

In a strongly worded attack, the former deputy Prime Minister said he feared Mr Johnson's “judgement is going” after he drew parallels between the EU project and the Nazis.

Lord Heseltine, who is one of the most respected figures within the party, said he would not be “very surprised” if Mr Johnson were to lead the Conservatives.

The former mayor of London, who has become the leading figurehead of the Brexit campaign, is touted as a successor to David Cameron should Britain vote to leave.

Lord Heseltine told the BBC: “I think that every time he makes one of these extraordinary utterances people in the Conservative Party will question whether he now has the judgement for that role.”

Mr Johnson said last week that throughout history, attempts to unify Europe under a single power had failed, citing Napoleon and Hitler. He said the EU “was an attempt to do this by different methods”.

Boris Johnson talks with Labour MP Gisela Stuart and Ukip's Douglas Carswell aboard the Vote Leave Battle Bus yesterday (Getty)

"When he (Boris Johnson) starts invoking the memories of Hitler, that has crossed the bounds of domestic debate," Lord Heseltine said.

"It was about the most manic nationalist aggressive destruction on a scale unprecedented in human history. It was about the persecution of the Jews. A calculated decision to persecute the Jews on a massive scale - that was what he wanted to do. He believed in it.

"The idea that a serious British politician can in any way invoke that memory, I find, frankly, I had better contain my language."

He also criticised what he called Mr Johnson's "near-racist remark" about President Barack Obama, referring to a newspaper column in which the former Mayor of London suggested Mr Obama's "part-Kenyan" background had inspired an "ancestral dislike" for Britain.

In response, a spokesman for Mr Johnson said: "What matters here are the arguments. The British people want to hear debate - they aren't interested in personality politics or personal attacks. Let's get on and discuss the issues."