In an extraordinary attack on his fellow Conservatives, Major produced a withering assessment of leading members of Vote Leave, calling their campaign deceitful, untrue, depressing, awful and “verging on the squalid”.
The former prime minister insisted his intervention was not a personal slight against Johnson or Gove, but a more general criticism of the leave campaign’s shift to the right on immigration and claims that they would protect the NHS.
However, he went on to claim Gove had wanted to privatise the NHS, Johnson wished to charge people for health services and Duncan Smith advocated moving to a social insurance system.
“The NHS is about as safe with them as a pet hamster would be with a hungry python,” Major said on BBC1’s The Andrew Marr Show.
He added Johnson was a “court jester” but not a serious politician and said that the Conservatives Johnson had divided would not be loyal to him after leaving the EU.
“I think I would offer him this piece of advice – if the leave campaign led by Boris continue to divide the Conservative party as they are doing at the present time, and if Boris has the laudable ambition, for it is a laudable ambition, to become prime minister, he will find if he achieves that that he will not have the loyalty of the party he divided.
“Iain Duncan Smith was serially disloyal in the 1990s, when he became leader he was surprised that no one was loyal to him and Boris should learn from that.
Turning to Vote Leave’s claims about the economy, Major said they were “fundamentally dishonest” about the cost of the EU being £350m a week.
“And on the subject that they have veered towards, having lost the economic argument, of immigration, I think their campaign is verging on the squalid,” he said.
“I am angry at the way the British people are being misled, this is much more important than a general election, this is going to affect people, their livelihoods, their future, for a very long time to come and if they are given honest, straightforward facts and they decide to leave, then that is the decision the British people take.
“But if they decide to leave on the basis of inaccurate information, inaccurate information known to be inaccurate, then I regard that as deceitful.”
The attack, which was likely to have been authorised by the official remain campaign and Downing Street, is designed to counter the Vote Leave claim that it would spend at least £100m more a week on the NHS out of money clawed back from Brussels.
Leading Brexit campaigners reacted by taking a serious tone in interviews on Sunday morning, rather than launching a counterattack on Major. In an interview with Peston on Sunday, Gove said he still believed the party could come back together after a vote to leave, and he would not want to choose between his close allies Cameron and Johnson.
He also argued that the UK will not actually have left the EU by 2020 in the event of a vote for Brexit, implying there will be a long time period to get the negotiations right.
“We wouldn’t have left the European Union by the end of this parliament but we would in due course bring [immigration] down to tens of thousands,” he said.
A backbench Brexit campaigner, Bernard Jenkin, tweeted that his side was “rising above the personal attacks and bitterness of John Major, with positive case for leave”. Andrea Leadsom, a Conservative energy minister, told the BBC 5 Live’s Pienaar’s Politics: “He’s obviously decided playing the man is going to be the better tactic for the remain side.”
Speaking on Marr as well, Johnson dismissed Major’s accusations and said he wanted to talk about the arguments.
The former London mayor said it was “absolute nonsense” that he was supporting the leave campaign out of personal ambition and added that he did not want it to become about “personality politics”.
He also distanced himself from a Vote Leave poster that said: “David Cameron cannot be trusted on immigration,” claiming he had never seen it before.
Major’s attack is the latest escalation of hostilities between leading Conservative members of the in and out campaigns, which have engaged in vicious claims and counterclaims in the last few weeks.
Johnson has previously accused the prime minister of leading a government that had eroded trust on immigration by failing to meet its targets.
On Sunday, he wrote jointly with Gove in the Telegraph that the prime minister had put the British economy in “severe danger” by giving away a UK veto during talks in Brussels earlier this year.
Other leading members of the leave campaign have more directly impugned the prime minister’s character, painting him as untrustworthy and damaged as a leader.
Three backbench Tory MPs have suggested he should face a leadership challenge after the referendum, and more could speak out if he continues to campaign so ferociously to stay in the EU.
Duncan Smith last week accused Cameron of insincerity and an attempt to deceive the public over EU immigration.
From the other side, Michael Heseltine, a Conservative former deputy prime minister, accused Johnson of behaving “irresponsibly [and] recklessly” and making “preposterous, obscene political remarks”.
Ken Clarke, a Tory former chancellor and home secretary, said Johnson was not serious and just a nicer version of Donald Trump, while Nick Clegg, the Lib Dem former deputy prime minister, said on Friday that the former London mayor was like “Trump with a thesaurus”.
Despite the bitterness of the rows, the prime minister told the Mail on Sunday that he would want Johnson and Gove to have major roles in the government if Britain voted to stay in.
He also warned that quitting the EU would create a “clear and present” danger of rocketing mortgage costs by £1,000 on average or £1,500 in the worst-case scenario.
This article was written by Rowena Mason Political correspondent, for theguardian.com on Sunday 5th June 2016 12.46 Europe/Londonguardian.co.uk © Guardian News and Media Limited 2010