The prime minister's Brexit negotiator, Olly Robbins, told her the Irish border backstop arrangement within her agreement with the EU represents a "bad outcome" for the UK, it has emerged.

In a letter to Theresa May, as seen by The Daily Telegraph, Olly Robbins warned the backstop - aimed at avoiding a hard border on the island of Ireland - would mean the imposition of regulatory checks between Northern Ireland and the rest of the UK.

The prime minister's chief Brexit adviser said: "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."

Chakrabarti: PM risking constitutional crisis

The top civil servant, who took on responsibility for negotiations with Brussels earlier this year, is also reported to have used the 19 October letter to tell Mrs May there is no legal "guarantee" the UK will be able to escape the backstop arrangement, if it comes into force.

Mrs May hopes the UK will agree a trade deal with the EU before the end of the Brexit transition period in December 2020 in order to avert falling into the backstop, or even extend the transition period if negotiations on the future UK-EU relationship drag on beyond that date.


However, the backstop provision has been included in the UK's withdrawal agreement as an insurance policy in case either of those scenarios don't happen.

The emergence of Mr Robbins's letter to the prime minister, said to have been leaked by a "concerned" minister, has further fuelled demands for the government to release the full legal advice on Mrs May's Brexit deal.

Attorney General Geoffrey Cox will address MPs on Monday, but the government have promised only to release a "full reasoned political statement" on the legal advice.

This is despite the House of Commons last month backing a motion to ensure the government would be required to lay before parliament "any legal advice in full", including that of Mr Cox.

Tory MP and former Brexit minister David Jones said: "At this crucial moment in the Brexit process, it is essential that parliament should be as fully informed as possible on the legal issues surrounding the deal.

"These include, among others, the role of the European Court of Justice, the justiciability of the 'best endeavours' provision and whether it is possible to withdraw from the backstop without the consent of the EU."

Opposition parties are threatening to launch contempt of parliament proceedings against ministers over the issue.

Who is Theresa's May's 'Brexit brain'?

Labour's shadow attorney general, Baroness Chakrabarti, told Sky News: "If the government does not comply with the order the House of Commons passed on 13 November, that would be a very serious matter indeed - almost a constitutional crisis."

Even the DUP - which props up the minority Conservative government at Westminster - is said to be ready to help prompt contempt proceedings together with Labour, which would pile yet more pressure upon the prime minister with little more than a week to go before parliament votes on the deal she struck last month.

'Inevitable' no-confidence motion for May

Further criticism of Mrs May's deal is likely to come after the BrexitCentral website published an assessment by House of Commons legal officials which reportedly states a UK-EU customs union, as part of the backstop, would be "a practical barrier to the UK entering separate trade agreements on goods with third countries".

US President Donald Trump recently criticised the prime minister's deal for hampering the possibility of a US-UK trade agreement.

Corbyn: I don't agree with BBC debate format

Mrs May will make her own statement to MPs on Monday following last week's G20 summit.

Home Secretary Sajid Javid dismissed reports the government could pull a vote on the Brexit deal, scheduled for 11 December, amid expectations it will be rejected by MPs.

He told the BBC: "I don't think there is any chance of pulling the vote... I just don't see that happening."

Mr Javid also admitted it is "very unlikely" the government's plan for a post-Brexit immigration system will be published before the House of Commons vote.

Shadow Brexit secretary Sir Keir Starmer told Sky News it is "inevitable" Labour would try to oust Mrs May if she loses the vote, which will come two days after the prime minister is due to take part in a TV debate with Jeremy Corbyn.

There is still disagreement over the format of the programme, with the Labour leader indicating that he will only go with the Conservatives' preference for a BBC debate if it is a straight head-to-head.

The BBC wants leaders to take questions from a wider panel and Downing Street has accused Mr Corbyn of "running scared" by so far refusing to sign up.

Neither of the BBC or ITV proposals have proved popular with other parties, with Sir Vince Cable accusing both of excluding other viewpoints.

In a letter to Sky, the BBC and ITV, the Liberal Democrat leader said: "The principal alternative to the withdrawal agreement is for the UK to remain as a full and influential member of the European Union."

PM appeals to public for Brexit deal support

Leading Brexiteers, including Boris Johnson, former Brexit secretaries David Davis and Dominic Raab, have also written to broadcasters to criticise the planned debate.

They claim neither Mrs May nor Mr Corbyn, who both backed Remain at the 2016 EU referendum, "can be said by any interpretation of their positions to be backing a plan that will deliver on the mandate of the 17.4million who voted Leave".

Their letter adds the views of Leave supporters "will be nowhere represented in this prime time debate".

There will also be no room on the debate podium for SNP leader Nicola Sturgeon, who is travelling south to London on Monday in a bid to persuade MPs to try and secure an extension to Article 50.

May hounded from all sides over Brexit deal

However, Environment Secretary Michael Gove said on Sunday he believed the government could still win the parliamentary vote next week.

Mr Gove, one of the leaders of the Leave campaign in the 2016 referendum, urged fellow Brexiteers to back the agreement warning the alternative was "no deal or no Brexit".

He said that if the government lost the vote there was a "real risk" there could be a majority in the Commons for a second referendum.