EU deal: David Cameron urged to sign 'take it or leave it' clause as Donald Tusk says talks may be extended until Sunday

France and Belgium are demanding that David Cameron signs up to a ‘take it or leave’ clause in Britain’s renegotiation settlement that would close down the option of a second renegotiation should voters reject the current deal being thrashed out in Brussels.

Talks between Mr Cameron and his European counterparts continued long into the early hours, pushing back hopes that a final resolution may come at a Friday morning breakfast.

Under plans put forward at a meeting of EU leaders any agreement would contain wording making clear that the deal represented the EU’s ‘final offer’ to Britain and could not be re-opened in the event of a ‘leave’ vote.

Senior British Government sources suggested that such a ‘self destruct’ clause might be acceptable to Mr Cameron “depending on the precise wording”.

It would allow the Prime Minister to go into the referendum with the clear message that voting to leave would mean just that – and not, as some leave campaigners have suggested, the opportunity to get a better deal in the future.

“The idea is to kill the idea of a second referendum,” said one eurozone diplomat involved in talks.

The clause would also attempt to deter copycat “exception seekers” by making clear that other member states could not use Britain’s deal as a precedent for their own renegotiation demands in the future.

Any final deal is not expected to be signed of by the EU’s 27 leaders until at least lunchtime, and there are currently a significant number of unresolved issues to be thrashed out.

European Council president Donald Tusk has said the summit could be extended until Sunday if an agreement was not reached today.

Among them are the plans to limit child benefit payments to the off spring of migrant workers. Mr Cameron wants to impose the restrictions immediately - including for existing migrants - while Eastern European countries are arguing it should be phased in for new workers.

British Government sources made clear that this would be unacceptable.

“If that happened some payments could go on for 16 years,” they said.

During the discussions, Mr Cameron told fellow EU leaders that he saw the prospect of a deal as an “opportunity to settle for a generation Britain’s place within the EU”.

He said the agreement would create a fundamentally different type of union where member states would “live and let live” allowing some to integrate more fully while other countries like Britain had their “interests” as members of the single market “protected”.

But in an attempt to prevent early drafts of the deal being watered down in the final negotiations Mr Cameron made clear that the agreement had to be “credible” to the British people.

Downing Street is well aware that he needs to come out of the talks without too many further concessions. In particular he wants to secure agreement that key elements of the text will be incorporated into EU treaties when they are next revised. This is being currently opposed by some countries as “unnecessary”.

Arriving head of the talks Mr Cameron said he would not accept a deal at any price.

“Well we’ve got some important work to do today and tomorrow and it’s going to be hard,” he said.

“I’ll be battling for Britain, if we can get a good deal I’ll take that deal but I will not take a deal that doesn’t meet what we need.”

The German Chancellor Angela Merkel said she believed a deal was possible as did the French President Francois Hollande. But he added: “No country must have a right of veto, no country must exempt itself from the common rules or common authorities. It's the European Union that's at stake, not simply one country of the European Union.”

Jean-Claude Juncker, the European Commission president, said he remained “quite confident” that a deal would be reached in spite of there being “a number of questions” still to answer.

Dalia Grybauskaite, Lithuania’s president, predicted “everybody would have [their] own drama - and then we will agree”.

But Nigel Farage, who spent the afternoon in the European Council building briefing journalists said he expected Mr Cameron to come back with a deal – but an inadequate one.

”He hasn't asked for us to get back supremacy for our Parliament, he hasn't asked for us to control our own borders, he hasn't asked to reduce the vast daily fees we pay.

“We will be allowed - after he has come here like Oliver Twist and begged for concessions - to control migrant benefits for up to four years. I find the whole thing as a British person pretty shameful.

”And the worst bit is that whatever he comes back with and tries to sell to the British people is not legally binding. It can be struck down by the European Parliament and ultimately all of it can be ruled out of order by the European Court of Justice.

“It's rather like him saying to the British people, 'I'd like you to buy this car, but you can't see whether the engine works first'. It just doesn't work.”