The British government unveiled a draft Brexit law on Wednesday to rewrite parts of its EU withdrawal deal, prompting the EU to call for urgent talks.

The EU has voiced concerns that the proposed legislation will breach the binding divorce treaty, which British MPs approved by a majority of by 358 votes to 234 in December.

Downing Street said its new UK Internal Market bill could change post-Brexit customs and trade rules in Northern Ireland. The bill would give the UK government the right to unilaterally change some of the arrangements made for the UK's only land border with the EU.

Britain agreed to meet the EU over the implementation of the revised deal, a UK government spokesperson confirmed, after Brussels urgently called on such a meeting to clarify "strong concerns" over the latest alterations.

The spokesperson also blamed the speed with which the initial deal was arranged, for the change of tack, citing "ambiguities" with the original version.

Read more: Will Boris Johnson sink Britain's Brexit withdrawal deal?

A question of trust?

The announcement has angered the 27 EU governments. They believe it breaches commitments made to protect the peace process and avoid a hard border on the island of Ireland.

"Clearly, any unilateral departure from the terms of the Withdrawal Agreement would be a matter of considerable concern and a very serious step," Irish Foreign Minister Simon Coveney said.

"Such a departure could seriously erode and damage political trust, not only in the Brexit negotiations."

Germany said it "fully expects" the UK to respect international law.

"We would continue to trust the British government to fully implement the exit agreement," German Foreign Ministry spokeswoman Maria Adebahr told reporters in Berlin, which currently head the Council of the European Union.

Ursula von der Leyen, the president of the European Commission, warned the UK that implementing the withdrawal agreement was "an obligation under international law and prerequisite for any future partnership."

She added that any deviation from the withdrawal agreement, however minor, would "break international law and undermine trust."

The European Union warned Britain that even the most minor breach of the treaty would undermine what little trust is left between the two sides in already fragile trade talks.

"Breaking international law is not acceptable and does not create the confidence we need to build our future relationship," European Council President Charles Michel said.

Brandon Lewis, the British government's minister for Northern Ireland, told parliament on Tuesday that the proposed legislation would "break international law in a very specific and limited way."

What is being proposed?

Last year, the British government agreed that Northern Ireland would need to follow EU rules on goods.

The EU argued that installing any border infrastructure at the frontier between Northern Ireland and Ireland would breach the Good Friday Agreement that ended decades of conflict in the region.

It meant that Downing Street accepted that there would be a customs border down the Irish Sea.

Under the divorce treaty, Northern Irish businesses would need to fill out customs forms when shipping goods to mainland Britain. Checks would be carried out on goods in the other direction.

Ministers say the new law will define specific circumstances when the UK can override parts of the withdrawal agreement it ratified last year.

The government says it will be able to unilaterally decide which goods are "at risk" of entering the EU.

The big issues

This week's talks are the eighth round of negotiations between the UK and the EU aimed at securing a relationship without tariffs and or customs checks.

The EU's chief Brexit negotiator Michel Barnier told French radio on Monday that he was "worried" about the chances of sealing a trade deal because the UK still wants "the best of both worlds."

His British counterpart, David Frost, said Tuesday the EU needs to show "more realism" and accept the UK's desire to be a sovereign state.

Disagreements still remain on future access to British waters for European fishing fleets and state aid.

Britain left the EU in January and faces a race against time to agree a free trade deal before the end of the transition phase on December 31.

They will have to fall back on World Trade Organisation rules if no agreement is struck, which will mean new tariffs, border checks and other barriers to trade.

ed, jf, jsi/sms (Reuters, AFP)