LONDON (AP) — With 18 months until Britain is due to leave the European Union, the U.K. government warned lawmakers on Thursday that it would be "reckless" to oppose a key piece of Brexit legislation.

Meanwhile, the EU's chief negotiator said he was worried by some of the suggestions coming from the U.K. on a deal over Ireland, and voiced concerns Britain was backpedaling on its financial commitments to the bloc.

British lawmakers began debate on the European Union (Withdrawal) Bill, which aims to convert some 12,000 EU laws and regulations into domestic statute on the day the country leaves the bloc in March 2019. The legislation is a key plank in the government's plans to disentangle Britain from the EU after more than four decades of membership.

Brexit Secretary David Davis said that "without this legislation a smooth and orderly exit is impossible" and delaying or opposing the bill would be "reckless in the extreme."

The government says that once EU laws have been incorporated into the U.K. statute book, they can be kept, amended or scrapped by Britain's Parliament, fulfilling the promise of anti-EU campaigners during last year's referendum to "take back control" from Brussels to London.

Critics say the bill gives the government worrying powers, because it allows ministers to fix "deficiencies" in EU law without the parliamentary scrutiny usually needed to make or amend legislation. Such powers are often referred to as "Henry VIII powers" after the Tudor king's bid to legislate by proclamation.

Opponents worry the Conservative government could use such powers to water down environmental standards, employment regulations or human rights protections.

Keir Starmer, the Brexit spokesman for the opposition Labour Party, said the legislation would more accurately be named "the great power-grab bill."

"So much for taking back control," he said.

Labour says it will vote against the bill when it is put to lawmakers on Monday.

Britain is due to leave the EU in March 2019, two years after it triggered the official exit process.

Exit negotiations have made little headway, with the EU and Britain accusing one another of failing to compromise. Davis has urged EU negotiators to show "flexibility and imagination" and begin negotiating on a future economic relationship that would include a free trade deal between Britain and the bloc.

The EU says that can't happen until substantial progress has been made on divorce terms, including the amount Britain must pay to settle its financial commitments to the bloc.

While lawmakers started debating the EU bill, the EU's chief negotiator Michel Barnier said that the former British prime minister, David Cameron, had signed up to the EU's seven-year budget in 2013 and that Britain would have to honor the promise.

Estimates of what Britain owes have ranged from 40 to 60 billion euros ($48-72 billion), but British officials have refused to say how much the U.K. is willing to pay.

Barnier told reporters in Brussels that he was "disappointed" by recent British statements on the Brexit bill, which seemed to retreat from previous commitments.

Barnier also said he was worried by some of Britain's proposals on another key issue, the status of the Ireland-Northern Ireland border.

He said a "unique" solution would be needed to ensure there was no return to a hard border between EU member Ireland and Northern Ireland, which is part of the U.K.

And he warned that the EU would not allow Britain to use Ireland as "a kind of test case" for future customs arrangements.

"This will not happen," Barnier said.

EU officials have accused British negotiators of being slow and unfocused in their approach to the talks.

Britain wants to move on to the second stage of talks, on future relations in October. But Herman van Rompuy, a former European Council president, said Thursday that the chances of that happening are "in the neighborhood of zero."

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Casert reported from Brussels.