The 1972 European Communities Act will not be fully repealed until the end of the planned transition period, at the end of 2020 – rather than on exit day next year.
Dominic Raab, the Brexit secretary told MPs the move was necessary to “ensure the statute book functions properly....in accordance with the agreement we have made with the EU”.
But it is certain to enrage pro-Brexit MPs – who had been promised the 1972 Act, which took the UK into the then-common market, would be scrapped in March 2019.
It is certain to provoke protests that the UK has not really left the EU next year – and will require amending the EU Withdrawal Act, passed into law only last month.
The move also raises possibility of legal challenge, because Britain will be stripped of Euro-MPs and EU commissioners yet remain under the Brussels rulebook.
It could also trigger louder calls for the Article 50 period to be extended, beyond next March, as a more straightforward mechanism for the reality of transition.
In the Commons, Steve Baker, who resigned as a Brexit minister in protest at the Chequers plan, demanded to know that MPs would be given a vote on reinstating the 1972 Act.
Keir Starmer, Labour’s shadow Brexit secretary, said the government had been left amending its own flagship legislation even “before it comes into force”.
He told MPs it was a “huge understatement” on Mr Raab’s part to suggest only parts of the 1972 Act would have to be “saved” until 31 December 2020 – arguing “almost all of it” would be affected.
“Just a few weeks ago many Brexiteers cheered section 6(1) of the Withdrawal Act extinguishing the role of the European Court on the fixed day of the 29 March 2019 - and not so fast,” Sir Keir said.
And he added: “I can't remember legislation which has needed such great revision and amendment before the relevant parts have even come into force.”
As Mr Raab was speaking, the prime minister confirmed Whitehall’s worst-kept secret by confirming the downgrading of his Brexit department in the negotiations.
In a written statement, she announced: “I will lead the negotiations with the European Union, with the Secretary of State for Exiting the European Union deputising on my behalf.
The Brexit department would only be responsible for “domestic preparations”, including for a no deal outcome.
Mr Raab also provoked anger when he was asked if EU nationals living in the UK will be allowed to stay if the UK and EU fail to strike a withdrawal agreement.
The Brexit secretary said only that there would be “no wholesale removal of rights of EU nationals in this country”.