The DUP branded the Brexit deal 'economically mad' today after secret legal advice revealed the extent of the border down the Irish Sea created by the Irish backstop.

Nigel Dodds, the party's leader in Westminster, said the document was 'devastating' after the Government finally published it today after being humiliated in the Commons last night.

The six-page memo drawn up by Attorney General Geoffrey Cox for the Prime Minister says the backstop leaves Northern Ireland treating Britain as a 'third country' in some cases.

And goods passing from Britain to Northern Ireland would have to undergo 'regulatory checks' during the backstop.

Mr Cox's advice also said the backstop is 'intended to subsist even when negotiations have broken down' - meaning it has been designed to last forever if talks fail.

After the paper was published, the Prime Minister was accused of 'misleading' the Commons as she returned to the Despatch Box for PMQs.

SNP Westminster leader Ian Blackford said the politically spun version of the advice on Monday has 'concealed the facts' - prompting a furious row with the Speaker as MPs are not allowed to accuse each other of lying.

Mrs May insisted there was nothing new in the secret letter because both she and Mr Cox had openly said the backstop was 'indefinite' without a final trade deal.

Earlier, MPs were warned by Commons leader Andrea Leadsom they would live to 'regret' forcing the Government to publish the letter.

The latest blow to Mrs May comes after yesterday's historic triple defeat in the Commons lobbies.

In the worst defeat, 26 Tory rebels sided with Labour to push through an amendment that would let MPs step in if her deal is defeated next Tuesday.

The five-day Brexit deal debate will continue this afternoon after it adjourned at just after 1am this morning.

Britain could be stuck in the Irish backstop forever if trade talks with the EU break down, the Prime Minister (pictured in Downing Street today) was warned in secret legal advice

The document, drawn up by Attorney General Geoffrey Cox (pictured in the Commons yesterday) for senior ministers, said the measure is 'intended to subsist even when negotiations have broken down'.

Theresa May was back at the Despatch Box today (pictured) for PMQs today despite the bruising day in Parliament yesterday

In his letter, Mr Cox said 'despite statements in the Protocol it is not intended to be permanent and the clear intention of the parties that it should be replaced by alternative, permanent arrangements, in international law the protocol would endure indefinitely until a superseding agreement took its place'.

63 minutes of mayhem: how May was defeated three times in an hour Theresa May suffered the worst day of any Prime Minister in 40 years in the Commons yesterday as MPs inflicted three defeats on her in barely more than an hour. This is how it unfolded: 4.41pm: The first vote is announced on the Government's amendment to the contempt motion, attempting to kick it into the long grass. Government loses 311 to 307. 4.58pm: The main Labour motion declaring the Government to be in contempt of Parliament is announced. Government loses 311 to 293. It is the first time in history Parliament has done this. 5.44pm: Dominic Grieve's amendment on what happens after the deal is rejected is announced. Government loses 321 to 299. It means when the PM sets out the next steps after losing the vote on the deal, Parliament can re-write the plan with its own priorities for the first time. 5.48pm: Theresa May stands up to make the case for her deal at the Despatch Box. Advertisement

This suggests the backstop has been drafted to last even if talks break down naturally, rather than if one side deliberately stalls them.

The Attorney said the deal 'does not provide for a mechanism that is likely to enable the UK lawfully to exit the UK wide customs union without a subsequent agreement'.

This section makes clear it is impossible for Britain to escape the backstop unilaterally and a political deal with Brussels was the only way out

Mr Cox said 'this remains the case even if parties are still negotiating many years later and even if the parties have believe that talks have clearly broken down and there is no prospect of a future relationship agreement'.

The letter says goods moving between Britain and Northern Ireland must be subject to a 'declaration process'. It said Britain would be 'essentially treated as a third country' by Northern Ireland.

In his conclusion, Mr Cox advises the Prime Minister there is a 'legal risk the United Kingdom might become subject to protracted and repeated rounds of negotiations' because it was giving up the ability to walk away without escaping the backstop.

He said: 'This risk must be weighed against the political and economic imperative on both sides to reach an agreement that constitutes a politically stable and permanent basis for their future relationship.

'This is a political decision for the Government.'

The secret legal advice was contained in a six page note from the Attorney General Geoffrey Cox to the Prime Minister on November 13 titled the 'legal effect of the protocol on Ireland/Northern Ireland'

The letter says goods moving between Britain and Northern Ireland must be subject to a 'declaration process'. It said Britain would be 'essentially treated as a third country' by Northern Ireland - something which has enraged unionists

In the letter, Mr Cox said the 'protocol is intended to subsist' - meaning last forever if negotiations on a final trade deal break down

Mr Cox told the Prime Minister the deal offered no legal way out for the UK short of a political deal with the European Union

Mr Cox said the legal risks of the deal must be 'weighed against the political and economic imperative on both sides'

Following the letter's publications, Mr Dodds said the advice was 'devastating' to the Prime Minister's claims about the deal.

Who are the 26 Tory rebels who voted for Dominic Grieve's amendment? Here are the 26 Tory rebels who voted for Dominic Grieve's amendment which allows MPs to tell the Government what to do in Brexit talks if the PM's deal is voted down Heidi Allen, South Cambridgeshire Guto Bebb, Aberconwy Richard Benyon, Newbury Nick Boles, Grantham and Stanford Kenneth Clarke, Rushcliffe Jonathan Djanogly, Huntingdon Michael Fallon, Sevenoaks George Freeman, Mid Norfolk Richard Graham, Gloucester Damian Green, Ashford Justine Greening, Putney Dominic Grieve, Beaconsfield Sir Oliver Heald, North East Hertfordshire Jo Johnson, Orpington Phillip Lee, Bracknell Jeremy Lefroy, Stafford Sir Oliver Letwin, West Dorset Nicky Morgan, Loughborough Bob Neill, Bromley and Chislehurst Antoinette Sandbach, Eddisbury Sir Nicholas Soames, Mid Sussex Anna Soubry, Broxtowe John Stevenson, Carlisle Derek Thoma, St Ives Ed Vaizey, Wantage Sarah Wollaston, Totnes Advertisement

He said: 'This advice concisely sets out the stark reality of the operation of the backstop.

'Its publication demonstrates how the Prime Minister has failed to abide by the commitments she gave in that the United Kingdom as a whole would leave the European Union and that she would ensure there would be no customs or regulatory divergence within the United Kingdom.

'This backstop is totally unacceptable to Unionists throughout the United Kingdom and it must be defeated and arrangements renegotiated that uphold the commitments which the Prime Minister and her government has in the House of Commons.'

Shadow Brexit Secretary Sir Keir Starmer said: 'All this advice reveals is the central weaknesses in the Government's deal.

'It is unthinkable that the Government tried to keep this information from Parliament and indeed the public before next week's vote.'

Earlier today, Mrs Leadsom told the Today programme the Government was furious at being forced to publish.

She said: 'It was incredibly disappointing that the House of Commons decided to vote in effect to overturn what has been decades, if not centuries, of conventions whereby the law officer's advice to Cabinet and to ministers are not even acknowledged, let alone published.

'The Attorney General had come to the House for two-and-a-half hours, which is also unprecedented in these many years, to answer questions to give his very best legal advice.

'He published a 48-page document that outlined all of the legal impact of the Withdrawal Agreement, so the vote yesterday of the House to require the specific legal advice to Cabinet we will comply with, but not without some regret.'

Mrs Leadsom continued: 'Going forward, not only will Government ministers be very careful about what they ask law officers to give advice on, but law officers themselves will be very reluctant to give any advice to Government that they might then see published on the front pages of the newspapers.

Who were the Tory MPs who rebelled to hold the Government in contempt? The Government lost two votes on whether it was in contempt of Parliament last night - first on its own amendment trying to kick the issue into the long grass and then on the main Labour motion. Two Conservative MPs rebelled each time: Peter Bone Philip Hollobone In the second vote on the main Labour motion, 11 Tory MPs went missing - meaning a heavier defeat for the Government. Advertisement

'So it's the principle of the thing.

'And frankly I think any parliamentarian who wants at some point in the future to be in Government is going to live to regret their vote last night.'

'And frankly I think any parliamentarian who wants at some point in the future to be in Government is going to live to regret their vote last night.'

Mrs Leadsom said the impact of Mr Grieve's amendment could make a no deal Brexit both more and less likely, depending on how MPs react.

She said MPs should vote for Mrs May's deal because while it was not perfect was the 'best combination we are going to get'.

Admitting she was unhappy with the Irish border backstop, she insisted it was also 'not in the EU's interest' for Britain to be locked into it indefinitely.'

Former Brexit secretary Dominic Raab said it would be 'inconceivable' to stop the UK leaving the EU, saying it would be wrong to 'pull a handbrake up on Brexit'.

Following the letter's publications, DUP Westminster leader Nigel Dodds said the advice was 'devastating' to the Prime Minister's claims about the deal

He told BBC Radio 4's Today programme the deal is 'lousy', and said: 'If the deal is voted down on Tuesday I think what will matter most of all will not be what Parliament says in a motion - it will need legislation to stop Brexit - what will matter is the will and resolve in Number 10 Downing Street.'

What is in the secret version of the Brexit legal advice? The backstop is designed to be permanent Mr Cox said: 'Despite statements in the Protocol it is not intended to be permanent and the clear intention of the parties that it should be replaced by alternative, permanent arrangements, in international law the protocol would endure indefinitely until a superseding agreement took its place.' This suggests the backstop has been drafted to last even if talks break down naturally, rather than if one side deliberately stalls them. Britain cannot exit the backstop without a trade deal The deal 'does not provide for a mechanism that is likely to enable the UK lawfully to exit the UK wide customs union without a subsequent agreement'. This section makes clear it is impossible for Britain to escape the backstop unilaterally and a political deal with Brussels was the only way out There is no escape even if trade talks break down On leaving the backstop, Mr Cox said: 'This remains the case even if parties are still negotiating many years later and even if the parties have believe that talks have clearly broken down and there is no prospect of a future relationship agreement.' This means the backstop will continue even if talks fail without either side breaking promises to pursue them in 'good faith' and with 'best endeavours. Goods passing between Britain and Northern Ireland must be checked Mr Cox said: 'Goods passing from GB to NI will be subject to a declaration process... The implications of NI remaining in the EU single market for goods while GB is not is that for regulatory purposes GB is essentially treated as a third country by NI for goods passing from GB to NI.' This is a regulatory border down the Irish Sea, something the DUP and other Unionists insist Mrs May promised she would never allow. Talks might never end Mr Cox concludes: 'There is a legal risk the United Kingdom might become subject to protracted and repeated rounds of negotiations' because it was giving up the ability to walk away without escaping the backstop. This risk must be weighed against the political and economic imperative on both sides to reach an agreement that constitutes a politically stable and permanent basis for their future relationship. 'This is a political decision for the Government.' This is Mr Cox repeating his warning that Brexit is not really a legal question but a political judgement about the risks and benefits of a particular course of action. Advertisement

Mrs May's ailing hopes of winning the vote on Tuesday took another blow today as former chief whip Mark Harper joined the ranks of Tory MPs pledged to vote No.

Mr Harper demanded the PM 'listen to Conservative colleagues' and tell Brussels to strip the Irish border backstop out of the deal.

Last night, Mrs May tried to keep her plan alive with a rousing speech to the Commons, in which she warned 'Brexit could be stopped' entirely if it is voted down on Tuesday.

She acknowledged criticism of her 'compromise' deal, but said: 'We should not let the search for the perfect Brexit prevent a good Brexit that delivers for the British people.

'And we should not contemplate a course that fails to respect the result of the referendum, because it would decimate the trust of millions of people in our politics for a generation.'

Dominic Grieve, the former attorney general, led the rebellion which could effectively takes a no-deal exit off the table.

He claimed it could lead to a second referendum, adding: 'MPs are tonight starting the process of taking back control.'

Downing Street must now hope that the threat of Parliament blocking a no-deal Brexit convinces some Eurosceptic opponents of her deal to change their minds before the meaningful vote.

However, a number of high profile, and previously loyal, Tory MPs rebelled during the series of defeats last night – including Michael Fallon and Damian Green.

And in a clear indication that the Prime Minister's 'confidence and supply' deal with the DUP is fractured beyond repair, the Northern Irish party warned her it did not fear another election.

Downing Street had hoped the threat of a general election would bring the DUP to heel, because it could bring the pro-Nationalist Jeremy Corbyn to power.

But the party voted against the Government last night, with Nigel Dodds, the party's Westminster leader, telling Mrs May his party was ready to spark another poll. He added: 'I'm certain we will be returned in greater numbers.'

In her speech last night the PM admitted that both Remainers and Brexiteers have been left dissatisfied by parts of her deal.

But she said the 'hard truth' is that the compromise she has thrashed out with Brussels is the only deal which delivers on the historic vote and protects jobs.

She said: 'I know there are some in this House and in the country who would prefer a closer relationship with the European Union than the one I'm proposing, indeed who would prefer the relationship that we currently have and want another referendum.

'Although I profoundly disagree, they are arguing for what they believe is right for our country and I respect that.

'But the hard truth is that we will not settle this issue and bring our country together that way and I ask them to think what it would say to the 52 per cent who came out to vote Leave, in many cases for the first time in decades, if their decision were ignored.'

What happened in the day of drama in the Brexit battle? By Jack Doyle What happened yesterday? The Government lost three votes in a day, the first time that has happened since 1996 – an ominous date for the Tory Party which went on to face catastrophic electoral defeat the following year. The first two were on the Brexit legal advice given to Cabinet by Attorney General Geoffrey Cox. They were damaging, but not disastrous. The third, which is potentially much more significant, was on an amendment, proposed by leading Remainer Tory rebel Dominic Grieve, setting out what could happen if Theresa May's deal is voted down next week. It could, in theory, give MPs vast leverage over the next steps on Brexit. Why is the legal advice vote significant? Last month the Commons demanded the full legal advice be published. Ministers refused. Yesterday MPs voted to declare this decision a contempt of Parliament – a serious form of legal admonishment. To avoid the prospect of ministers being suspended by the House, the Government rolled over and agreed to release the document today. No 10 fought tooth and nail to resist publishing, warning to do so would be 'against the national interest' and breach historic conventions. To placate MPs, Mr Cox made a statement to Parliament describing what it said and published a summary. Much of the document will be familiar, but it will make plain the gravity of Mr Cox's warnings about the UK being trapped in the Northern Ireland backstop, potentially hardening opposition to the deal among rebel Tory MPs. What does the Grieve amendment mean? Following an earlier row this summer, Mr Grieve won a concession that if the deal falls, the Government will have to come back to the Commons within three weeks to set out what course it will then take. As a result of yesterday's vote, MPs will now be able to propose what alternative course of action the Government should take by making amendments to the motion and voting on them. Almost inevitably, the likely proposals will include the UK staying in a permanent customs union, or membership of the single market, or both – or a second referendum. For its supporters, this makes 'no deal' impossible as the Commons – which is overwhelmingly opposed to crashing out – would immediately make clear its disapproval. Some hardline Brexiteers deny this, arguing that any amendment would not be legally binding on the Prime Minister. In theory this is true, but any such vote would heap huge political pressure on the Government to comply. Where does this all leave us? With nearly 100 MPs publicly expressing their doubts about the deal, its chances of passing on Tuesday already appeared slim. Losing a string of votes exposes just how weak Mrs May's grip on a fractious and volatile Parliament has become. With this in mind, the Grieve amendment could be hugely significant. If it is seen to reduce the chances of a no-deal Brexit, could it yet convince hardline Eurosceptic rebels they should back Mrs May's deal? Or will they press on, with the danger that the future of Brexit falls into the hands of a Remain-dominated Parliament which is flexing its muscles more every day and could yet find a way to sink Brexit altogether? Advertisement

The PM added: 'There are others in this House who would prefer a more distant relationship than the one I'm proposing and although I don't agree, I know they're also arguing for what they think is best for our future and I respect that too.

'But the hard truth is also that we will not settle this issue and bring our country together if in delivering Brexit we do not protect the trade and security cooperation on which so many jobs and lives depend, completely ignoring the views of the 48 per cent.

Mrs May said the 'only solution that will endure' is one that addresses the concerns of both sides of the debate.

But she faced a fiery Commons session as leading Brexiteers lashed her plan, while the DUP - who are propping the Tories up in No10 - said they would be happy to have another general election.

Boris Johnson, who has become the PM's fiercest critic since quitting as Foreign Secretary over her Brexit plan, said the deal is a failure.

He told the Commons: 'I can't believe there is a single member of this House who sincerely believes that this is a good deal for the UK.

'You can tell that the government's hearts are not in it

'You can tell that they know it is a disaster because after two and a half years this deal has done an amazing thing it has brought us together – remainers and leavers in the belief that it is a national humiliation that makes a mockery of Brexit.

'There will be no proper free trade deals. We will not take back control of our laws and for the government to continue to suggest otherwise is to do violence to the normal meaning of words.

'We will give up £39bn for nothing. We will not really be taking back control of our borders.'

While Nigel Dodds, the DUP's Westminster leader has said he would be 'happy' to have another general election to prove the party has support in Northern Ireland for blocking the PM's Brexit deal.

He said: 'We will happily go to the electorate and put our views to the people if needs be, and I'm quite certain we would be returned in greater numbers than today.'

A slew of MPs had condemned ministers for refusing to release the full Brexit deal legal advice in a fiery Commons showdown today.

It had pitted Mrs May's authority and support against the accumulated strength of her opposition - which spanned both Brexiteers and Remainers.

But admitting defeat and announcing the legal advice will be published tomorrow, Mrs Leadsom said: 'We have tested the opinion of the House twice on this very serious subject...

'We will publish the final and full advice provided by the Attorney General to Cabinet.'