EU law will stop applying in Britain after 31 October, legislation signed into force today ensures.
Brexit Secretary Steve Barclay rubber-stamped the move to repeal the European Communities Act that automatically transfers laws made into Brussels into UK statute.
He hailed the moment as sending a “clear signal to the people of this country that there is no turning back”.
But a legal expert downplayed the significance of the moment, saying if Brexit is delayed again then European law will continue to apply until the UK leaves the EU.
Mr Barclay was pictured posing for a photo showing the moment he signed the regulation into law.
“We are leaving the EU as promised on 31 October, whatever the circumstances – delivering on the instructions given to us in 2016,” he said.
It had already been passed in parliament as part of legislation paving the way for Brexit in June last year.
But to be legally enforced it needed signing off by a minister in what is called a “commencement order”.
Mr Barclay said doing so “ensures” EU law will cease to take precedence over British law and apply here after the Brexit date in less than 80 days.
“This is a landmark moment in taking back control of our laws from Brussels,” he added.
But Mark Elliott, a professor of public law and chair of the faculty of law at the University of Cambridge, said the announcement was “at best, misleading”.
He said on Twitter that the 1972 European Communities Act “will only be repealed on ‘exit day.'”
“If parliament forces the government to seek, and the EU grants, an Article 50 extension, the definition of ‘exit day’ can be altered & ECA repeal deferred accordingly,” said Prof Elliott.
“So repeal isn’t ‘set in stone’.”
Labour MP Stephen Doughty, who is campaigning for a referendum on the terms of Brexit, also dismissed its significance.
He told Sky News: “I do not believe [Brexit] is inevitable.
“I think it’s only right that the British people should have a say in that.
“They now know what this particular prime minister wants to do, which is crash out with no-deal.”