Theresa May's chief Brexit adviser secretly warned her that the Northern Ireland "backstop" agreed in her deal with Brussels was a "bad outcome" for Britain, it has been reported.
In a letter to the Prime Minister, Oliver Robbins said the backstop, intended to prevent the return of a hard border with the Republic, would mean the imposition of regulatory checks between the North and the rest of the UK, according to The Daily Telegraph.
The disclosure will add to the pressure on the Prime Minister at the start of another difficult week as she battles to save her Brexit deal ahead of the crucial Commons vote on December 11.
- Read more: Universities minister resigns over Theresa May’s Brexit deal
- Read more: There will be no-deal or no Brexit at all if Parliament rejects PM's deal, says Donald Tusk
The Telegraph said it had been passed details of the letter by a "concerned minister", and reported that Mr Robbins had advised there was no legal "guarantee" Britain would be able to exit the backstop, potentially leaving the UK tied to EU customs arrangements.
He was said to have written: "We should not forget that the backstop world, even with a UK-EU customs union, is a bad outcome with regulatory controls needed somewhere between GB and NI, serious and visible frictions and process between GB and the EU, and no security co-operation provided for."
Contempt of parliament threat
The leak is likely to intensify demands for the Government to release the full legal advice on the Withdrawal Agreement if it is to avoid a major constitutional battle with parliament.
Attorney General Geoffrey Cox will on Monday attempt to head off a threat by opposition parties to initiate proceedings against the Government for contempt of parliament.
- Read more: John McDonnell begins to prepare for Treasury takeover in case of 'government collapse' over Brexit deal vote
Ministers have been accused of ignoring the will of the House after saying they will publish only a "full reasoned political statement" on the legal position concerning the Withdrawal Agreement.
Sir Keir Starmer. Image: Getty
Shadow Brexit secretary Sir Keir Starmer has warned Labour will join with other opposition parties in writing to Speaker John Bercow to initiate contempt proceedings if the advice is not released.
Worryingly for ministers, Labour says it has the support of the DUP - who prop up the Government in the Commons - as well as the SNP and the Liberal Democrats, while many Tory MPs are also demanding to see the advice.
In his weekly column in The Daily Telegraph, Boris Johnson said it was a "scandal" that ministers were withholding the full advice.
"It is outrageous that the public should be prevented from knowing the full legal implications of this appalling deal - when it is their rights, their freedoms, their hard-won suffrage, that are about to be bartered away," he said.