BORIS Johnson and EU leaders gave their Brexit negotiators four more days to get a deal as they warned that “very large gaps” remained between the two sides.

After three hours of “frank” discussion in Brussels between the Prime Minister and Ursula von der Leyen, president of the EU Commission, Downing Street said it was “unclear” whether the remaining differences could be bridged.

The two leaders gave their teams until Sunday to reach an agreement but said that if a deal was not possible by then, a “firm” decision would have to be taken to suspend talks and prepare for a Brexit without one.

“The Prime Minister does not want to leave any route to a possible deal untested,” a Downing Street source told The Times, adding: “Very large gaps remain between the two sides and it is still unclear whether these can be bridged.”

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The European side struck a more optimistic tone, suggesting that the dinner between Johnson and Von der Leyen had been constructive and friendly.

“There is a lot to be done but a deal is still possible,” a source said.

Von der Leyen said: “We had a lively and interesting discussion on the state of play across the list of outstanding issues. We gained a clear understanding of each other’s positions. They remain far apart. We will come to a decision by the end of the weekend.”

In other developments:

• Sir Keir Starmer, the Labour leader, hinted his party might back a deal, promising to vote “in the national interest”.

• British tourists to EU nations face an increase in travel insurance premiums to plug a £156 million annual shortfall in the cost of medical treatment, according to research.

• Ministers were warned that disruption at British ports would be exacerbated in there is a no deal Brexit.

The impasse came before an EU summit in Brussels today which Downing Street hopes will unlock talks, with a no-deal looming in three weeks.

France is resisting moves to soften EU demands.

The Prime Minister and Von der Leyen worked during the dinner of scallops and turbot from an agreed document detailing between 20 and 30 issues on which the talks had become stuck.

They were joined by the two chief negotiators David Frost and Michel Barnier as well as Oliver Lewis, Lord Frost’s deputy, and Stéphanie Riso, deputy head of Von der Leyen’s cabinet.

The National:

Arriving for the dinner Johnson was reprimanded by Von der Leyen for not keeping his distance when he walked too near her as she welcomed him to the European Commission. As he got out of his car, she ushered him in with the words allons-y or “let’s go”.

When Johnson asked if they were taking off their masks for the cameras, she replied “yes” but “keep distance” as they posed for pictures.

“Then we have to put it back on,” she added. “You have to put it back on immediately.”

The meeting came as Johnson warned that no prime minister could accept EU demands on so-called level playing field provisions as the price of a free trade agreement. He said that Brussels must drop proposals to punish Britain if it failed to follow future EU environment and social protections.

In the Bundestag Angela Merkel, the German chancellor, said that as British and EU laws diverged, it was imperative that Brussels could prevent unfair competition. “We need to have a level playing field not only for today, but for tomorrow, and the day after that,” she said.