Theresa May is facing a battle to save her Brexit plan amid claims the European Union has rejected a key proposal.
Talks with Brussels have reportedly broken down over the PM’s solution to the Irish backstop.
The current proposal would see the whole of the UK remaining in a temporary customs arrangement to avoid a hard border between Northern Ireland and the Republic.
To allay fears this would leave the UK trapped indefinitely in a customs union – Mrs May had drawn up a mechanism which would allow the UK to leave the backstop.
Using the legal expertise of Attorney General Geoffrey Cox, it proposed using an independent arbitration panel.
But the EU has reportedly dismissed this plan, dubbed the Cox compromise, insisting any arbitration must come from the European Court of Justice.
This would be a huge blow for the PM’s hopes of reaching a deal with Brussels by the end of the month.
Mrs May had also hoped her solution would bring together her divided cabinet at a meeting this week.
Meanwhile speculation grows over the possibility of other resignations, following the departure of transport minister Jo Johnson.
Mr Johnson warned Britain was on the brink of the greatest crisis since the Second World War.
Throwing his support behind a second referendum, he added it would be a travesty not to let voters have their say on the final deal.
Another four Remain MPs are said to be considering their positions.
Any more resignations could cost the government valuable votes when any deal comes before parliament.
Brexiteers and the DUP have joined forces warning they will vote down any deal which prioritises the EU over the UK.
Steve Baker, the deputy chairman of the European Research Group of Tory backbenchers, and DUP Brexit spokesperson Sammy Wilson have said they would oppose any agreement at the price of our union.
The Labour leadership says it is highly unlikely it will vote for the government’s current plan.
Writing in the Sunday Times, shadow Brexit secretary Sir Kier Starmer says he will work with other parties to stop a no-deal scenario.
He said: Labour will stick to its guns. Supporting a bad deal is not in the national interest. So, we have to be clear that if the prime minister’s deal is rejected, parliament must take back control. There is no mandate for a no-deal.