Britain was on the edge of a no-deal Brexit as Ireland vowed to “never” sign an agreement without the Northern Ireland backstop – and Eurosceptic MPs said they might reject the deal regardless.

Irish Deputy Prime Minister Simon Coveney’s stark warning to Boris Johnson came as backbench Tory Eurosceptics signalled that, even if ministers could remove the hated customs insurance policy, they will vote down the current Brexit deal anyway.

The deadlock facing the prime minister at home and abroad crystallised on a day of high drama at Westminster, as Johnson was branded a “tin pot dictator” over his highly controversial decision to suspend parliament. 

The Commons will now be shut down between September 9 and October 14, leaving MPs who on Monday agreed to unite to block no-deal scrambling for time. 

Speaking in Paris, Coveney said Ireland will not compromise on the backstop as it risked jeopardising “a peace process that is fragile” in Ireland. 

“Now we have a British government who seems to be wiping the slate clean on the Irish issue,” he said. “We can never sign an agreement with that approach.

“We’ve always said if there is to be a no-deal Brexit it will be the choice of a British prime minister and British government that will make that happen.

“We’re not going to compromise on a peace process that is fragile right now on the island of Ireland.

“A peace agreement that has saved lives and that has created normality between communities that in the past were in conflict.”

Mark Francois, the deputy chairman of the backbench Brexiteer faction of Tory MPs known as the European Research Group, also had bad news for Johnson.

He told ITV’s Paul Brand that ERG MPs may still vote down the Brexit deal if the only part to change were the backstop. 

Francois said that Johnson had promised backbenchers that Theresa May’s deal, which includes a £39bn divorce bill, was “dead”.

Asked if he would back an amended version, Francois said: “No. Prior to the first parliamentary ballot – when Boris was all desperate for the ERG to vote for him – he had a meeting in the room next door to here with the senior leadership of the ERG and he absolutely, adamantly promised us that the withdrawal agreement was dead.

“He said it several times. Now, if a politician makes an absolute commitment, to me, I expect them to keep their word whether they’re a prime minister or a parish councillor.

“So … I’m not voting for the withdrawal agreement and I suspect neither will many of my colleagues.”

Johnson, a leading figure in the Vote Leave campaign in 2016, has always insisted that he wants to strike a new deal with Brussels, but that “do or die” the UK would exit the bloc at Halloween. 

Coveney said Brexit would have a “disruptive impact” and the UK and EU had  “a shared responsibility” to preserve peace in Ireland. 

He added: “We can’t give up on something that we know works on the back of a promise without any idea as to how it’s going to work.”

Coveney downplayed the lack of an official visit and face-to-face meeting between Johnson and the Irish Prime Minister Leo Varadkar, but stressed that talks between the UK and Ireland had been fruitless so far. 

“They have spoken over the phone and prime minister Johnson is due to come to Dublin in early September, so that meeting is going to happen soon,” he said. 

“It would be wrong to say the British and Irish governments haven’t spoken.

“I have spoken to Steve Barclay a number of times, I’ve spoken to Dominic Raab and Julian Smith as there is, of course, an ongoing conversation between Britain and Ireland – but that isn’t delivering an agreement.”