Britain and the European Union traded ill-tempered barbs on Tuesday as the UK said a Brexit deal might be impossible, with just over three weeks until its scheduled departure from the bloc.

Key points: Angela Merkel said that a deal was "overwhelmingly unlikely", according to Downing Street

Angela Merkel said that a deal was "overwhelmingly unlikely", according to Downing Street Any deal depends on Northern Ireland remaining in the EU's custom union, she reportedly said

Any deal depends on Northern Ireland remaining in the EU's custom union, she reportedly said The Labor Party said Boris Johnson was trying to "sabotage the negotiations"

British Prime Minister Boris Johnson's office said EU intransigence had led to a breakdown in negotiations, prompting a top European leader to warn against playing a "stupid blame game" — and chide Mr Johnson in Latin.

Mr Johnson's office gave a gloomy assessment after a call between the Prime Minister and German Chancellor Angela Merkel on Tuesday morning.

In a statement to British media, Downing Street said Ms Merkel had told Mr Johnson that a deal was "overwhelmingly unlikely" unless the UK agreed to allow Northern Ireland to continue to follow EU customs rules in order to maintain an open border with EU member Ireland.

That's something the British government says it cannnot accept. Downing Street said that "if this represents a new established position, then it means a deal is essentially impossible not just now but ever."

How people and goods will move across the Irish border is the main sticking point in a deal.

The German government confirmed Ms Merkel and Mr Johnson had spoken but declined to comment on the substance of "confidential conversations".

European Commission spokeswoman Mina Andreeva said "the EU position has not changed. We want a deal. We are working for a deal with the UK."

European Council President Donald Tusk tweeted testily that "what's at stake is not winning some stupid blame game".

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"At stake is the future of Europe and the UK as well as the security and interests of our people," he said, addressing Mr Johnson.

"You don't want a deal, you don't want an extension, you don't want to revoke, quo vadis?" — a Latin phrase meaning "where are you going?"

Irish Deputy Prime Minister Simon Coveney tweeted that it was "hard to disagree" with Mr Tusk's statement, saying it reflected "frustration across EU and the enormity of what's at stake for us all".

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EU leaders have demanded more "realism" from Britain in response to a Brexit plan proposed by Mr Johnson. The bloc says the proposals — which would require customs checks on some goods moving between Northern Ireland and Ireland — don't fulfill the UK's commitment to a frictionless Irish border.

Mr Johnson has urged the bloc to compromise but also insists the UK will leave the EU on October 31 even without a deal.

French President Emmanuel Macron has said the EU will assess by Friday whether a deal is possible.

Mr Johnson's opponents in Britain accused the government of deliberately undermining the Brexit talks. Keir Starmer, Brexit spokesman for the main opposition Labour Party, said the Downing Street statement was "yet another cynical attempt by No. 10 to sabotage the negotiations," using the shorthand for the prime minister's office.

"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.

Scottish First Minister Nicola Sturgeon, who opposes Brexit, 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."

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On Tuesday, Britain published more details of its plans for a scenario where there is no deal. The government says those plans will minimise any resulting economic shock.

Economists and business groups warn that no amount of preparation can eliminate the pain of new barriers with the EU, which accounts for almost half of UK trade.

The government's "no-deal readiness report" shows significant British preparation but also acknowledges its limits. Britain says it will try to keep goods flowing by not immediately imposing border checks on imports from the EU. But the government acknowledges there will be new tariffs on 60 per cent of British exports to the EU, including levies of more than 50 per cent on beef and lamb.

Many in the EU — and in Britain — are sceptical that Britain will leave the bloc on October 31 because the UK Parliament has passed a law compelling the government to ask the EU for a delay to Brexit if no deal is agreed upon by that October 19.

Boris Johnson urged the EU to hold "rapid negotiations towards a solution" on Brexit. ( AP: Kirsty Wigglesworth )

Parliament is set to be suspended later today so that a new session can begin next week with a major policy speech from Mr Johnson's Conservative government.

The British government said Tuesday that the chances of a Brexit deal with the European Union were fading fast. ( AP: Kirsty Wigglesworth )

An earlier attempt by the government to shut down Parliament for five weeks was ruled illegal by Britain's Supreme Court because it had the effect of preventing Parliament from scrutinizing the government's Brexit plans. This week's shorter suspension is more routine. MPs will return on Monday.

Many are anticipating an early election. Both the government and the opposition see a national vote as the only way to break Britain's Brexit deadlock, though they disagree on the timing.

AP