Hours after a Brexit deal collapsed, British Prime Minister Theresa May came under pressure yesterday from opposition parties and even some allies to soften the EU divorce by keeping Britain in the single market and customs union after Brexit.

May's ministers said they were confident they would soon secure an exit deal, though opponents scolded the prime minister for a chaotic day in Brussels which saw a choreographed attempt to showcase the progress of Brexit talks collapse at the last minute.

The Northern Irish party that props up May's minority government said it was only shown the draft of a deal promising regulatory alignment for both parts of Ireland late on Monday morning.

In a sign of just how politically precarious May's Brexit balancing act has become, the Democratic Unionist Party (DUP) also said it had warned May that it would not support her legislation in parliament unless the draft was changed.

The opposition Labour Party said one way for alignment of Northern Ireland with the Republic of Ireland to become acceptable was for the whole of the United Kingdom to stay in the single market and the customs union.

Nicola Sturgeon, the leader of Scotland's devolved government, said May's failure could signal a push to keep Britain in both.

Scottish Conservative leader Ruth Davidson, who has been tipped as a potential future leader of May's party, also suggested May should consider keeping the United Kingdom in the single market and customs union.

May has repeatedly said Britain will leave both groupings when the United Kingdom ends its membership of the EU at 2300 GMT on March 29, 2019.