Boris Johnson may have ruined his chances of becoming prime minister by behaving “irresponsibly [and] recklessly” and making “preposterous, obscene political remarks” during the referendum campaign, the Conservative former deputy prime minister Michael Heseltine has said.

In a remarkably pointed and personal intervention Lord Heseltine, a remain campaigner, said he would now be very surprised if Johnson became prime minister and that the strain was beginning to show on the former mayor.

Referring to the former London mayor’s comments at the weekend comparing the EU integration project to Hitler’s attempt to conquer Europe, Lord Heseltine told the BBC that Johnson had “crossed the bounds of domestic debate. 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 any serious British politician can in any way invoke that memory, I find – frankly, I had better contain my language.



“He is behaving now irresponsibly, recklessly and I fear that his judgment is going.”



Heseltine has been working closely with the Britain Stronger in Europe campaign, which will raise questions over whether his comments have been sanctioned by Downing Street.



Speaking to the BBC, the Tory grandee said: “I find it deeply distressing. I don’t really understand what Boris is up to, frankly. I know him, I like him, he makes me laugh. And yet [his comments] about Hitler – I found that deeply disturbing.”

The EU, he said, “has been an incredible political change to 28 free democracies voting together. And Boris can talk about Hitler? ... I think the strain of the campaign is beginning to tell on him. I think his judgment is going. Before that we had the near-racist allegations about President Obama. This is the most serious decision Britain has faced in a generation. And it is descending into an extraordinarily nasty situation”.

Asked if Johnson could still be Tory leader, Heseltine said: “Every time he makes these extraordinary utterances I think people in the Conservative party will question whether he now has the judgment for that position.”

In another day of increasingly pointed accusations and counter-accusations, Johnson accused David Cameron on Tuesday of “what looks like collusion” with big business leaders to win their support for the remain campaign in exchange for favourable consideration in the awarding of government contracts.

Commenting on a leaked letter from the chief executive of outsourcing giant Serco to the prime minister, which referred to discussions over how to persuade firms to publicly back staying in the EU, Johnson said on Tuesday “questions need to be asked and answered” about “the commitment by that company to support remain and any possible contracts that that company may secure”.



“When you have what looks like collusion between the government and big remain-backing businesses, it seems to be suggesting that in exchange for support for remain there’s consideration given to the awarding of lavish public sector contracts. I think we need a full explanation of that without delay.”



Johnson had earlier described the correspondence between Serco CEO Rupert Soames and the prime minister, which took place while Cameron’s negotiations over a new EU deal were still ongoing, as “the biggest stitch-up since the Bayeux tapestry”, adding: “It makes us look like a banana republic.”



Elsewhere on Tuesday, Cameron suggested in a speech that Abu Bakr al-Baghdadi, the leader of Isis, was probably in favour of Britain leaving the EU.



In a speech to the World Economic Forum, Cameron said: “It is worth asking the question: who would be happy if we left? Putin would be happy. I suspect al-Baghdadi would be happy.”



Cameron has previously argued that staying in the EU is vital for Britain’s security as it enables greater sharing of intelligence about terrorist activity across the bloc.

Responding to his comments about al-Baghdadi, Johnson said: “You might argue that it was a bit much to start comparing people who are arguing for freedom in this country ... to say that we are allies of Putin and Daesh, I think that’s a bit much, frankly.”

The former mayor of London was speaking on Tuesday during a visit to an aluminium processing plant in Staffordshire, where he burned a cheque for £350m in the plant’s blast furnace to symbolise the amount of money the leave campaign says Britain pays the EU every week. He was accompanied by the Ukip MP, Douglas Carswell, and Gisela Stuart, the Labour MP who chairs the official Vote Leave campaign.

Arguing that the leaked Serco letter revealed Cameron’s negotiations for an improved EU deal to be a meaningless “mime”, Johnson told reporters: “It really casts doubt over the sincerity of the negotiations. It was perfectly obvious from quite a while back the government was determined to campaign for a remain vote and I am afraid that contaminated the negotiations, because we then didn’t get a bean, a sausage, from our counterparts in the EU.”

In the letter, obtained by the Daily Mail and dated 8 February, Soames writes: “Thank you for a very useful meeting last week. There were two points I thought I might follow up on. The first is how to mobilise corporates to look carefully at the risks Brexit represents.

“I am working with Peter Chadlington and Stuart Rose [the head of Britain Stronger in Europe] with a view to contacting FTSE 500 companies who have annual reports due for publication before June and persuading them that they should include Brexit in the list of key risks.”

The newspaper does not reproduce the letter in full, but says Soames goes on to argue that it was a “wasted opportunity” that only 15% of the prisons market is run by the private sector.



Serco, which holds multimillion-pound government contracts for outsourced public services and operates six prisons in the UK, has denied there is any link between its support for the EU and any attempt to secure state contracts. A spokesman said last night it would not comment further on the leaked letter.

Johnson also said it was difficult to guarantee the EU question will be settled forever by the referendum, even though David Cameron has ruled out the idea of a second poll in future.

He said there was a difficulty in saying the question would be settled permanently because the British people might find it hard to accept the closer political union that Brussels is planning in future.

His comments followed remarks by Nigel Farage, the Ukip leader, that there could be an irresistible demand for a second vote if the 23 June referendum were only narrowly won by the remain campaign.



Cameron, in turn, responded by ruling out a “neverendum”, saying: “It is a once-in-a-generation, once-in-a lifetime opportunity and the result determines the outcome. If we vote to stay, we stay, and that’s it. If we vote to leave, we vote to leave, that’s it.”