Leading Brexiters have criticised the French president, Emmanuel Macron, for his extraordinary break in diplomatic convention in which he branded prominent leavers as liars who had misled the British people.

While Theresa May’s Chequers plan was left hanging by a thread after an ambush at the Salzburg summit, her French counterpart launched an unprecedented attack on Brexiters, warning that leaving the EU was “not without costs”.

Furious leavers immediately hit back, accusing Macron of trying to distract from his own domestic woes, with the former Tory leader Iain Duncan Smith telling him he should “butt out” of British politics.

Facebook Twitter Pinterest The hard-Brexiter Tory MPs Jacob Rees-Mogg, Boris Johnson and Iain Duncan Smith. Photograph: Dan Kitwood/Getty Images

After a key summit session at which the other EU leaders discussed the UK’s Brexit proposals, Macron had told reporters: “We are today at the moment of truth.”

He added: “Those who explain that we can easily live without Europe, that everything is going to be all right, and that it’s going to bring a lot of money home, are liars. It’s even more true since they left the day after so as not to have to deal with it.”

Duncan Smith told the Guardian: “Monsieur Macron is not only out of order, he’s completely wrong. The EU is doing their classic case of trying to bully the UK in a variety of ways into taking a different position.

“The honest truth is I don’t get involved in his domestic politics and therefore he should butt out of ours. He has got enough problems at home himself, it’s time he sorted his own country out and stopped messing around with ours.

“But it does open the door to remind people why so many voted to leave. They’re sick and tired of the dictatorial, bossy, lecturing nature of the European Union.”

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However, one Brexiter cabinet source shrugged off the criticism. “It’s just all part of ratcheting up the temperature, a bit of something for the home audience; it’s not something I’m particularly worried about,” he said. “At home, people don’t really care about what foreign leaders think – we learned that at the referendum.”

Macron has faced the biggest domestic scandal of his presidency after one of his security officials was filmed, illegally dressed as a police officer, beating people on the edge of a demonstration. The row grew when it emerged that the president’s office had been informed of the misconduct at the time but had not reported it to police.

Jacob Rees-Mogg, the chair of the hard-Brexit European Research Group of Tory MPs, said: “Is it an attempt to distract attention from the French senate interviewing his former bodyguard yesterday? It is not unknown for politicians to make outlandish claims to cover up a more interesting story.”

The Tory Brexiter Andrew Bridgen added: “It is a well-known British political truism that when you start insulting your opponents you have already lost the argument; perhaps we need to translate it into French?”