Theresa May’s hopes of securing House of Commons approval for her Brexit deal suffered a shattering blow as Tory eurosceptics said they would not back it and her DUP allies said they would vote against.
A so-called Star Chamber convened by the Leave-backing European Research Group found that agreements reached by the Prime Minister in 11th-hour talks in Strasbourg do not deliver the legally-binding changes the Commons has demanded.
And the Democratic Unionist Party – which props up Mrs May’s minority administration in the Commons – said its 10 MPs would vote against the latest deal as “sufficient progress has not been achieved at this time”.
Their judgment came after Attorney General Geoffrey Cox told MPs that changes secured by Mrs May “reduce the risk” that the UK could be trapped indefinitely in the backstop, but do not remove it altogether.
The Prime Minister, battling a croaky voice and with husband Philip watching from the Commons gallery, warned MPs that “Brexit could be lost” if her deal was rejected again by MPs.
She said it was “absolutely imperative” that Parliament should deliver on the decision made by voters in the 2016 referendum.
And she warned: “Tonight, members of this House are faced with a very clear choice. Support this deal, in which case we leave the EU with a deal, or risk no-deal or no Brexit. These are the options.”
Mrs May needs to win over scores of MPs to overturn the 230-vote majority which rejected her Withdrawal Agreement in the first “meaningful vote” in January.
But her prospects for doing so seemed bleak after the release of formal legal advice by Mr Cox
The Attorney General said the Strasbourg agreements “reduce the risk that the United Kingdom could be indefinitely and involuntarily detained” in the backstop if the EU fails to show good faith in negotiating a trade deal to replace it.
But he warned that the question of whether a satisfactory agreement on a future UK/EU relationship can be reached remains “a political judgment”.
And he said “the legal risk remains unchanged” that the UK may have “no internationally lawful means” of leaving the backstop without EU agreement.
In a statement to the Commons, Mr Cox told MPs: “There is no ultimate unilateral right out of this arrangement. The risk of that continues.
“But the question is whether it is a likelihood, politically.”
Shadow Brexit secretary Sir Keir Starmer said Mr Cox had confirmed that “no significant changes” had been secured in two months of negotiations and the Government’s strategy was “in tatters”.
Charles Walker, vice chairman of the 1922 Committee of backbench Tory MPs, warned that defeat in the second “meaningful vote” on Tuesday evening would lead to a general election.
He told BBC Radio 4’s World At One: “If it doesn’t go through tonight, as sure as night follows day, there will be a general election within a matter of days or weeks.
“It is not sustainable, the current situation in Parliament.”
Mr Cox’s advice was issued the morning after Mrs May’s dash to Strasbourg to finalise a deal with European Commission president Jean-Claude Juncker which she said would reassure MPs that the backstop arrangements to avoid a hard border in Ireland after Brexit will not become permanent.
The pair agreed a “joint instrument” setting out the legally-binding nature of their promises to seek alternative arrangements to avoid the need for a backstop, as well as a “supplement” to November’s Political Declaration making clear that they will seek swiftly to seal a deal on their new trade and security relationship.
Alongside these documents was a “unilateral declaration by the UK” which sets out “sovereign action” by which Britain could seek to have the backstop removed if talks break down.
In a statement to the Commons, Mrs May said she had “fought hard” to persuade the EU to accept a time-limit, a unilateral exit mechanism or alternative arrangements for the backstop.
But she told MPs: “Ultimately you have to practise the art of the possible. I am certain we have secured the very best changes that were available.”
She insisted: “A bad deal would be even worse than no deal, but best of all is a good deal – and this is a good deal.”
On a day of high drama in Westminster, the Cabinet gave its backing to the package, as Mrs May told them: “Today is the day. Let’s get this done.”
But momentum seemed to be shifting against the Prime Minister after Mr Cox released his advice.
Moments later, the Star Chamber issued its opinion: “Yesterday’s documents considered individually and collectively do not deliver ‘legally binding changes’ to the WA or to the (backstop) Protocol.
“They fail to fulfil the commitment made by Government to the House in response to the Brady amendment ‘to obtain legally binding changes to the withdrawal agreement’.”
A Conservative member of the group, Sir Bill Cash, said: “In the light of our own legal analysis and others we do not recommend accepting the Government’s motion today.”
In a statement the DUP indicated it would not support the deal, saying: “We recognise that the Prime Minister has made limited progress in her discussions with the European Union.
“However in our view sufficient progress has not been achieved at this time.”
Their decision is likely to be highly influential on many of the 118 Conservatives who rebelled in January, many of whom have voiced concern over the impact of the Withdrawal Agreement on Northern Ireland.
Senior Conservative Leaver John Whittingdale told the Commons Brexit Committee that the Attorney General’s advice was “pretty terminal” for Mrs May’s plan.
Brexit-backing Tory backbencher Andrea Jenkyns tweeted: “Nothing has really changed, and it is still a bad deal so unable to vote for this.”
Labour leader Jeremy Corbyn told the Commons: “After three months of running down the clock the Prime Minister has, despite very extensive delays, achieved not a single change to the Withdrawal Agreement.
“Not one single word has changed. In terms of the substance, literally, nothing has changed.”
Mr Juncker warned on Monday that if MPs voted down the deal a second time, “there will be no third chance”. And he said that any extension of the two-year Article 50 negotiation process could not go beyond May 23 unless the UK took part in European Parliament elections beginning that day.
MPs are expected to vote at 7pm, with Environment Secretary Michael Gove saying it is “make your mind up time”.