Boris Johnson has been told to stop playing a “stupid blame game” by European Council President Donald Tusk.

In an angry tweet directed at the prime minister on Tuesday morning, Tusk said the “future” of Europe and the UK was at stake, as the chances of a no-deal Brexit appeared to increase.

On Tuesday morning, following a phone call between Johnson and Angela Merkel, Downing Street accused accused Brussels of making it “impossible” for the UK to leave with a deal.

But Tusk hit back, accusing No.10 of trying to pin the blame for no-deal on the EU.

A No.10 source told several broadcasters that Merkel had made clear that a deal was “overwhelmingly unlikely”, unless the UK accepted that the Irish Republic must at least have a veto on Northern Ireland leaving the customs union – a position the British government has rejected.

The source is suspected to be Dominic Cummings, Johnson’s chief adviser.

A German government spokesperson confirmed the call took place but would not confirm Downing Street’s account. “As usual, we do not report from such confidential conversations,” the spokesperson told HuffPost UK.

Keir Starmer, Labour’s shadow Brexit secretary, said the briefing by No.10 was a “cynical attempt” to “sabotage the negotiations”.

“Boris Johnson will never take responsibility for his own failure to put forward a credible deal. His strategy from day one has been for a no-deal Brexit,” he said.

The PM’s official spokesman said that the call between Merkel and Johnson lasted 30 minutes and represented a “a frank exchange of views”. But he followed the convention of not briefing on what was said by foreign leaders in private phone calls.

No.10 did however hit back at Tusk’s accusation the UK was trying to blame the EU for no-deal. “Absolutely not. It’s not us talking in that language. It’s not the UK talking about blame games,” the spokesman said.

A source within the group of Tory rebels who were kicked out of the party for voting to block no-deal told HuffPost UK they believed Cummings was trying to “put on a show” of looking like the government was “genuinely pursuing a deal”.

“Then when that inevitably fails, blame the EU, and use it as justification for no-deal, claiming all along that you made a ‘fair and reasonable’ offer,” the source said.

“But there is nothing fair or reasonable about the offer from No10. It is a sham ‘deal’.”

“No.10 spent the summer preparing for an October election, and when that plan failed they rustled up something that looked vaguely coherent to a casual observer, and gave the appearance of ‘pursuing a deal’, but that they knew would never be acceptable since it clearly breached a number of red lines for the EU.

“No.10’s focus is not on negotiations, it’s on blame. They want to drag the country into a no-deal Brexit – blaming the EU for not engaging with their ‘deal’. But in reality there is no ‘deal’.”

The UK is due to leave the EU on October 31. Johnson has said he will take the country out with or without a deal.

But thanks to the Benn Act, passed by MPs opposed to no-deal, he will be forced to ask for an extension to the Article 50 process if an agreement is not reached by October 19.

On Monday night, a No.10 source told The Spectator that the Conservative Party was preparing to fight a snap general election on a “get Brexit done immediately” platform with a no-deal exit in order to “marginalise the Brexit Party”.

In a threat to EU member states, the source added: “Those who support delay will go to the bottom of the queue. Supporting delay will be seen by this government as hostile interference in domestic politics, and over half of the public will agree with us.”

Amber Rudd, who resigned from the cabinet and the Tory party last month, said she believed the source was Cummings. “It sounds angry and desperate. And the language that is used, I do not believe should be the language of a UK government,” she told BBC Radio 4′s Today programme.

In a sign of cabinet unrest over the aggressive stance, Julian Smith, the Northern Ireland secretary, said it was “unacceptable” for the UK to threaten to withdraw security cooperation from Ireland.

Smith’s tweet echoes concerns made by him and fellow cabinet minister Nicky Morgan during Tuesday’s cabinet meeting.