The Prime Minister's chief Brexit negotiator warned against backing a Tory plan to go back to Brussels and reopen negotiations in a series of emails to senior officials, The Telegraph has been told.

Oliver Robbins raised concerns about an amendment tabled by a senior Tory MP requiring the Prime Minister to secure changes to the Northern Ireland backstop, sources said.

He allegedly questioned whether the EU will be willing to make significant legal changes to the backstop. Mrs May, however, ultimately chose to back the amendment, which Parliament supported on Tuesday night by 317 votes to 301.

Mr Robbins is also said to have to have expressed concerns about the practicality of a "Plan C" to break the Brexit deadlock drawn up by Tory Remainers and Brexiteers, known as the "Malthouse compromise".

One source said: "The gist of the email was that it wasn't worth the paper it's written on."

Mrs May is facing a mounting backlash from Remain ministers over her plan to go back to Brussels and renegotiate her deal. One Cabinet minister told The Telegraph her plan was "insane... it is mad because we are trying to renegotiote our own deal."