Both Boris Johnson and Liz Truss are to vote against Rishi Sunak’s Brexit deal in Parliament.
The two former prime ministers will form part of an expected backbench rebellion against the agreement negotiated with Brussels, although the extent of Tory opposition remains unclear.
Johnson confirmed on Wednesday that he will not be backing the deal when MPs vote on the Stormont brake in the Commons later on Wednesday, with Ms Truss set to follow suit.
In a statement, Mr Johnson said: “The proposed arrangements would mean either that Northern Ireland remained captured by the EU legal order – and was increasingly divergent from the rest of the UK – or they would mean that the whole of the UK was unable properly to diverge and take advantage of Brexit.
“That is not acceptable. I will be voting against the proposed arrangements today.
“Instead, the best course of action is to proceed with the Northern Ireland Protocol Bill, and make sure that we take back control.”
A source close to Truss said she also plans to vote against it.
Commenting on the fallout, Tobias Ellwood said it is the inevitable conclusion of Brexit.
“There was always to be a problem, going back to the referendum. We have a land border with the EU.
“The people who did recognise this, ironically, were David Frost, Boris Johnson, Dan Hannah, Nigel Farage – they wanted to stay in the single market.”
Watch:
Related: Gary Lineker posts thinly veiled tweet ahead of Johnson’s Partygate probe