Former Prime Minister Sir John Major, who saw his own leadership of the country fatally damaged by infighting over the European Union (EU) has attacked “Britain’s most popular politician” for his campaigning to get Britain out of the EU.

Sir John’s attack came on the Andrew Marr show, as he dismissed Conservative Brexiteer and former London Mayor Boris Johnson as a “court jester”, and accused the Leave campaign of “squalid” behaviour.

He said: “What they have done … is feed out to the British people a whole galaxy of inaccurate and frankly untrue information,” he told the BBC, less than three weeks before the vote on June 23. “I think their campaign is verging on the squalid”.

“If they can’t be straightforward and honest on a clear cut matter of fact like that upon what else can we trust them,” he said, in his most outspoken intervention on the campaign.

“I think this is a deceitful campaign and in terms of what they’re saying about immigration, a really depressing and awful campaign, they are misleading people to an extraordinary extent.”

The intervention came within hours of Boris Johnson and Justice Secretary Michael Gove issuing a joint letter accusing the government of putting the nation in peril and claiming the public can no longer trust government promises over the European Union.

The letter said: “The Eurozone institutions remain broken and have been unable to cope with the euro’s crisis. Despite writing a promise of ‘no bail-outs’ into the EU Treaties, there have been massive bail-outs”.

“The Eurozone’s economic crisis is fueling the rise in migration. Millions of people in southern Europe, particularly young people, are giving up hope of their countries escaping recession. Unsurprisingly, migrants from those countries are disproportionately coming to Britain… These problems will only get worse when countries in the pipeline to join the EU become members in the near future.

“British taxpayers are already paying nearly £2 billion for Albania, Macedonia, Montenegro, Serbia and Turkey to join the EU. The European Commission recently announced an acceleration of these plans and is already extending visa-free travel to the border with Syria and Iraq. This is dangerous”.

Despite criticism from Britain’s political left and the Remain campaign for the Leave side bringing up the issue of immigration and Turkey’s accelerated accession to the EU, the issue has proven fertile ground for the campaign as the Europe migrant crisis has deteriorated.

Figures published last week put net migration at 330,000 in 2015, of which a net 184,000 came from the EU, far above Cameron’s ambition in 2011 to cut numbers to tens of thousands.

The Leave campaign has said it could extend an Australian-style points-based system to EU citizens if Britain votes to leave the bloc.

Justice Minister Michael Gove, a prominent Leave campaigner, said the scale of immigration was depressing wages and putting a strain on public services.

“We would in due course bring it down to tens of thousands,” he said on ITV’s Peston on Sunday show.

Johnson also deployed the “taking back control” argument on Sunday, in his case over the money Britain sent to Brussels, its borders and other parts of its economic future.

“It’s a question of democracy,” he said. “I would like a situation where the government can fulfil its pledges to the people.”

Sir John, whose 1997 defeat to Tony Blair’s New Labour was considered one of the worst results for the Conservative party ever and left No.10 in the hands of Britain’s political left for 13 years has been campaigning for Britain to remain in the EU.

Reuters contributed to this report