The government is due to set out how it plans to remove EU law from the statute book when it publishes details of its Great Repeal Bill later.
Having formally triggered Brexit, ministers are promising a “smooth and stable transition” with legislation ending the supremacy of EU judges.
It will also incorporate thousands of pieces of EU law into UK legislation.
The publication comes the day after the UK started two years of talks using Article 50 of the Lisbon Treaty.
Prime Minister Theresa May described the invoking of Article 50 as a “historic moment from which there can be no turning back”, saying Britain would now make its own decisions and its own laws.
She called for a “deep and special partnership that takes in both economic and security co-operation”, and also warned the failure to reach a deal could weaken the joint fight against crime and terrorism.
In response, Guy Verhofstadt, the European Parliament’s chief Brexit negotiator, said he would not accept any attempt to “bargain” between trade and security.
Asked if the PM’s comments amounted to “blackmail”, he replied: “I try to be a gentleman, so towards a lady I don’t even use or think about the word ‘blackmail’.”
Work and Pensions Secretary Damian Green told BBC Newsnight that Mrs May’s statement was “not a threat”, but a “sensible point to make” as new deals would be needed in a number of areas, including trade and security.
Key to the pledge of a post-Brexit Britain in charge of its laws is the Great Repeal Bill, which ministers say is essential to avoid a “black hole” in the law when the UK leaves the EU.
The UK Parliament can then “amend, repeal and improve” the laws as necessary, the government says.
However, it could prove controversial with plans to give ministers the power to make changes to some laws without full Parliamentary scrutiny.
The government says this will only be for “mechanical changes” to ensure laws function properly.
‘A unique challenge’
The Great Repeal Bill, which Theresa May has said will make the UK an “independent, sovereign nation”, would:
- Repeal the European Communities Act, which says EU law is supreme to the UK’s
- Ensure the UK leaves the jurisdiction of the European Court of Justice
- Transpose existing EU legislation into domestic UK law
- It would come into force the day the UK leaves the EU
- The Commons library anticipates it will be “one of the largest legislative projects ever undertaken in the UK”
- A Lords committee described it as a “unique challenge”, with EU law having accumulated over decades
Article 50 of the Lisbon Treaty gives both sides two years to reach agreement so, unless the UK and the 27 remaining EU member states agree to extend the deadline for talks, the UK will leave on 29 March 2019.
It was invoked through a six-page letter from Mrs May to EU Council president Donald Tusk, promising the UK would remain “committed partners and allies”.
Brexit Secretary David Davis said: “At the heart of the referendum decision was sovereignty. A strong, independent country needs control of its own laws. That process starts now.
“Converting EU law into UK law, and ending the supremacy of lawmakers in Brussels, is an important step in giving businesses, workers and consumers the certainty they need.”
The TUC urged the government to ensure the repeal bill was used to maintain all existing EU workers’ protections.
Foreign Secretary Boris Johnson admitted to popular “apprehension” over the outcome of a deal, but said Mrs May was “wise” to wait until now to set out her negotiating position.
He wrote in the Daily Telegraph on Thursday that Britain would continue to be “one of the indispensable guarantors of peace and stability” in Europe.
He added that the government did not want “divorce” from the EU but a “transition to a new relationship”.
Mr Tusk, who told the UK “we already miss you” as he received Mrs May’s letter, is expected to set out the EU’s draft negotiating principles in the coming days.
In a brief statement on Wednesday, he said it was not “a happy day” for him or for the EU and promised to begin arrangements for the UK’s “orderly withdrawal”.
The EU’s formal negotiating position will be agreed only at a summit of the remaining 27 member states at the end of April, meaning face-to-face discussions are unlikely until May or early June.
Early issues are likely to include the rights of expats in the UK and the rest of the EU, the size of any severance payment required of the UK and whether talks on a new trade deal can be handled at the same time as the Article 50 negotiations.
In a BBC interview after her Commons statement, Mrs May insisted the UK could keep “the same benefits” in terms of trade despite leaving the EU single market.
Labour’s Jeremy Corbyn said his party would be holding the government to account “all the way through”, promising to “speak for the entire country”.