Relations between the UK and the European Union last night entered a downward spiral as the imminent collapse of the Brexit talks triggered a bitter public blame game.

After a Number 10 source said Brussels had made a deal “essentially impossible” at next week’s EU summit, the bloc’s top official pointed the finger at Boris Johnson. EU Council President Donald Tusk tweeted directly at the Prime Minister, telling him the future of the UK and its people was at stake, “not winning some stupid blame game”.

The row was triggered by a Downing Street spin operation on the back of an early morning phone call between Mr Johnson and the German Chancellor Angela Merkel.

Number 10 told broadcasters Mrs Merkel had said Mr Johnson’s proposed alternative to the Irish backstop, which was only presented to Brussels last week, was “overwhelmingly unlikely” to work, raising the likelihood of a no-deal Brexit on October 31.

It also said her reported demand that Northern Ireland stay in the customs union had made a deal “essentially impossible, not just now but ever”.

The source told the BBC it had been a “clarifying moment”, adding: “Talks in Brussels are close to breaking down, despite the fact the UK has moved a long way.”

The Prime Minister’s official spokesman later confirmed there had been a “frank exchange” and said the UK’s talks with the EU over a deal had reached a “critical point”.

However there was anger and surprise on the EU’s side at the characterisation of the call, with Berlin refusing to comment officially on a “private” conversation, but diplomats stressing that Mrs Merkel would continue to work to the last moment to help get a deal.

Labour accused Downing Street of cynically trying to “sabotage” the negotiations and blame the EU for the failure of a proposal that had always been a non-starter.

First Minister Nicola Sturgeon tweeted: “The UK Government’s attempts to shift the blame for the Brexit fiasco to anyone but themselves – today it’s Merkel – is pathetically transparent.”

An incendiary Downing Street briefing, thought to be from the PM’s chief adviser Dominic Cummings, also heaped blame on Ireland for the failure of talks and a possible no-deal Brexit.

The source said that if the UK Government was forced by emergency legislation to extend Brexit past Hallowe’en, EU countries who promoted delay would then be punished.

Hinting at the possible withholding of defence and security co-operation, the source told the Spectator magazine: “Supporting delay will be seen by this government as hostile interference in domestic politics.

“We won’t engage in further talks, we obviously won’t give any undertakings about co-operative behaviour, everything to do with ‘duty of sincere co-operation’ will be in the toilet.”

The Tories would then campaign in a General Election for a no-deal Brexit, the source said.

Former home secretary Amber Rudd said the “angry and desperate” language pointed to Mr Cummings, as well as the lack of a clear Government plan.

As the recriminations flew, Mr Tusk addressed Mr Johnson on Twitter, telling him: “What’s at stake is not winning some stupid blame game. At stake is the future of Europe and the UK, as well as the security and interests of our people. You don’t want a deal, you don’t want an extension, you don’t want to revoke, quo vadis [where are you going]?”

Irish deputy leader Simon Coveney said it was “hard to disagree”, replying: “Reflects the frustration across EU and the enormity of what’s at stake for us all. We remain open to finalise a fair Brexit deal but need a UK Government willing to work with EU to get it done.”

The Taoiseach Leo Varadkar and Mr Johnson later spoke for 40 minutes by phone and are due to meet this week. However, after meeting Mr Johnson in Downing Street last night, EU Parliament President David Sassoli was downbeat, saying there had been “no progress” on a deal.

He said MEPs would “not agree to a deal at any price”, and described the UK plan to replace the Irish backstop as “a long way from something to which the Parliament could agree”, adding: “No deal would clearly be the responsibility of the UK Government.”

Mr Johnson has proposed keeping Northern Ireland aligned with EU single market rules, but taking it out the customs union, creating the need for controversial customs checks.

His plan also gives the Democratic Unionist Party a veto over the single market element. Mrs Merkel was reported to have told the PM a deal meant Northern Ireland staying in the customs union, creating an all-Ireland backstop. The DUP see that as splitting Northern Ireland from Great Britain.

Before Westminster was lawfully prorogued last night until October 14, shadow Brexit secretary Sir Keir Starmer told MPs: “The Government is intent on collapsing the talks and engaging in a reckless blame game.” But Cabinet Minister Michael Gove said there was still “every chance” of a deal, provided the EU engaged with the UK’s plans.

DUP leader Arlene Foster said: “The comments from the German Chancellor to the Prime Minister that Northern Ireland must remain in the EU customs union forever now reveal the real objective of Dublin and the European Union.

“For the United Kingdom to be asked to leave a part of its sovereign territory in a foreign organisation of which the UK would no longer be a part and over which we would have no say whatsoever is beyond crazy. No UK Government could ever concede such a surrender.”

Sinn Fein deputy leader Michelle O’Neill said: “What Boris Johnson proposed last week was a totally unworkable solution. It begs the question, is it more about political positioning in the run-in to an election? ”