Theresa May’s Brexit plans have been dealt a blow after the Democratic Unionist Party backed a rival plan drawn up by Tory rebels to allow the UK to leave the EU's single market and customs union without a hard border in Ireland.

The European Research Group published a paper calling for equivalence of UK and EU regulations and conformity assessment for all agricultural goods on the island of Ireland.

The plan - which is at odds with the Mrs May's Brexit proposal which was agreed by her Cabinet out at her Chequers country home - was immediately backed by the DUP, whose 10 MPs are keeping the Mrs May’s Government in power.

Nigel Dodds MP, the DUP’s deputy leader who met with Mrs May yesterday at 10 Downing Street, described the 18-page report as “a positive and timely development” that could deliver a “sensible Brexit”.

The document showed “there are sensible practical measures which can ensure there will be no hard border between Northern Ireland and the Irish Republic”.

The report’s publication was overshadowed by outspoken criticism of Mrs May and her leadership at a private meeting of the ERG on Tuesday.

One source said there were 50 Tory MPs in the room "just discussing the matter openly"and "war-gaming" how to get rid of the Prime Minister.