The EU will take Britain to the International Court of Justice if it tries to walk away without paying an estimated £50bn ‘divorce bill’, a leak of its negotiating strategy says.

The draft plan – obtained by a Dutch newspaper – threatens a long legal battle at The Hague to grab back what the EU regards as the UK’s liabilities for its 43-year membership.

“In that case it is: see you in The Hague!” it quotes an EU official – in response to Theresa May’s threat to leave with “no deal” if the Brexit talks cut up rough.

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The threat follows growing pressure on the Prime Minister from some Conservative MPs to simply walk away if the EU insists on imposing the huge exit fee.

Government lawyers have backed a report from a House of Lords committee which argued Britain could legally leave without paying up, if it accepts no withdrawal agreement.

But, yesterday, Britain’s ambassador to the EU, Sir Tim Barrow, warned Brussels had confidence in “other legal opinions” which reached a very different conclusion.

A lengthy battle at the International Court could also hold up attempts to reach a new trade agreement with the EU, if it insists on settling the controversy over money owed first.

The leak, published by the respected De Volkskrant newspaper, says the EU strategy will also:

* Insist access to the EU single market depends upon the UK accepting the ‘four freedoms’ – including, crucially, freedom of movement of citizens, a 'red line' for Ms May.

* Propose a deal guaranteeing both the future rights of EU nationals in the UK and Britons in EU countries.

* Demand that the UK loses some of its existing trade advantages, as the price of leaving.

* Consider whether to insist that talks on future trade deal will only take place after agreement on the exit deal - or sequentially, as the UK wants.

The newspaper billed its story as “the secret EU Strategy for separation from the British”, based on information provided by key EU insiders.

Only six people, including Donald Tusk, the European Council President, and Jean-Claude Juncker, the European Commission President, have seen the ten-page draft, it claimed.

The EU’s apparent strategy was published shortly after Mr Tusk announced that EU leaders will meet to agree their strategy at a special summit on April 29.

Significantly, he vowed to make "the process of divorce the least painful for the EU" - without mentioning what pain may lie ahead for Britain.

The De Volkskrant report suggested David Cameron is partly responsible for the expected £50bn EU demand being so high.

The former prime minister demanded cuts to the EU budget for 2014-20, but - in return for spending going down in the early years - planned spending in the future rose sharply.

The EU is expected to argue that the UK is obliged to contribute to those future spending commitments, despite its plans to complete Brexit by 2019.

David Jones, a minister in the Brexit department, has suggested the legal argument that Britain can walk away without paying a fee has “not gone unnoticed in Brussels and in other European capitals”.

But, giving evidence to MPs yesterday, Sir Tim Barrow sought to dampen Brexiteer enthusiasm to quit without paying “a brass farthing” as one Conservative MP put it.