In what seemed to be the first snag since May handed the EU official notice of the U.K.’s departure on Wednesday, Guy Verhofstadt, the chief EU negotiator in the Brexit process, criticized May for “threats” made in her letter.

“A big mistake that we could make from both sides is to start with launching threats to each other,” he told broadcaster Sky News.

“I find the letter of Mrs. May very constructive, generally, but there is also one threat in it, in saying ‘Look, we want also to cooperate with you on security issues in our common fight against terrorism but you have to give us a good deal on trade and economy.’

“It doesn't work like that -- you cannot use, or abuse, I should say, the security of citizens to have then a good deal on something else.”

In her letter invoking Article 50 of the Lisbon Treaty to initiate Brexit, May said a failure to reach a trade agreement at the same time as exit discussions “would mean our cooperation in the fight against crime and terrorism would be weakened.”

Brexit Secretary David Davis defended the prime minister against the charge that she had tried to “blackmail” the EU.

Speaking to BBC Radio 4, he said: “What the prime minister was saying was that if we have no deal, and we want a deal, it’s bad for both of us.

“If we don’t have a deal, what we are going to lose is the current arrangement on justice and home affairs.”

Meanwhile, following a telephone conversation with May, French President Francois Hollande stressed the need to focus on Britain’s “obligations” to the remaining EU members.

The negotiations must be held in a “clear and constructive manner, so as to lift uncertainties and to fully respect the rules and interests of the 27-member European Union,” he said in a statement released by the Elysee Palace.

It added: “The president indicated that the talks must at first be about the terms of withdrawal, dealing especially with citizens’ rights and obligations resulting from the commitments made by the United Kingdom.”

Government plans to change up to 1,000 EU laws

Meanwhile the government on Thursday published details of a plan to replace more than a thousand EU laws in Britain with domestic legislation.

The day after Prime Minister Theresa May initiated the U.K.’s EU exit, Brexit Secretary David Davis revealed the Great Repeal Bill to the House of Commons.

Many of the EU laws to be replaced concern workers' rights, environmental protection and consumer rights and critics fear these will be weakened as the bill will be passed without full parliamentary scrutiny.

The bill, which is expected to be one of the largest pieces of legislation in U.K. history, will transpose more than four decades of EU legislation into domestic law, repeal the European Communities Act and take the U.K. out of the European Court of Justice’s jurisdiction. It will come into force the day the U.K. leaves the EU.

“Once EU law has been converted into domestic law, parliament will be able to pass legislation to amend, repeal or improve any piece of EU law it chooses -- as will the devolved legislatures,” Davis said, referring to regional assembles in Wales, Scotland and Northern İreland.

Anadolu Agency