The European Union is poised to reject Theresa May’s demands for “legally binding assurances” that the Irish backstop will only ever be temporary, senior EU diplomats have told The Telegraph.

The EU rejection will come as another serious blow to the Prime Minister who was pinning her hopes of a legally-binding side-agreement with the EU to help convince her back-benchers to accept her Brexit deal.

EU ambassadors met in Brussels on to discuss how to respond to Mrs May’s pitch to leaders at Thursday’s summit dinner, where she will be given 10 minutes to outline what she needs to get the deal over the line in Westminster.

“Politically she can have all the warm words she wants, but it was very clear in the meeting that there is very little appetite indeed for anything legally binding,” said a senior EU diplomatic source.

The rebuttal came as Mrs May promised the backbench 1922 Committee that something legally binding on the backstop would be forthcoming.

Downing Street has previously promised a “legally binding” text, separate from the Withdrawal Agreement, that would commit the European Union to make every possible efforts to wind up the Irish backstop within one year, if it ever came into force.