Brussels - Britain has missed a one-month deadline to respond to a European Commission warning over an alleged breach of the Brexit withdrawal agreement, a spokesperson for the EU executive arm said on Tuesday.

Next steps are to be considered by the EU

The commission is now considering taking the legal action to the next level following Britain's failure to reply in time, spokesman Daniel Ferrie added.

The dispute centres on legislation proposed by Prime Minister Boris Johnson. The Internal Market Bill would override a provision in the EU-Britain divorce agreement that imposes different post-Brexit customs rules on Northern Ireland than the rest of the United Kingdom.

The EU argues that this goes against the terms of the agreement whereas Britain claims that the bill is necessary to protect the integrity of its internal market.

At the beginning of October, the commission launched legal action by sending a letter of formal notice to the British government.

Ferrie said the European Union had not received a response yet.

"Therefore we are considering next steps," he said, including escalating the legal procedure.

Brussels and London are currently racing against the clock to wrap up a post-Brexit trade deal both sides had said should already be finished by now to allow for ratification by the end of the year. Months of negotiations have yielded meagre progress.

 Great Britain and Northern Ireland in numbers

Britain has a chance until the end of this year

Britain remains in the EU single market until 2021, when the post-Brexit transition period ends. If no deal is struck, the imposition of tariffs and other trade barriers between the two mutually important commercial partners threatens to wreak havoc on businesses and supply chains.

EU chief negotiator Michel Barnier and his British counterpart David Frost are in intense talks this week in Brussels after Johnson threatened to walk away altogether last month.

The proposal of the Internal Market Bill in September further antagonized relations, which were already greatly strained by the two sides' differing visions of how closely London should be compelled to stick to EU regulatory standards and on fisheries, among other issues.

Asked for a reaction on the passed deadline, a British spokesperson said the government was "committed ... to find a satisfactory outcome for both sides."

"That is our overriding priority. We will respond to the next stages of this process in due course, as required," the spokesperson said.

At the launch of the infringement procedure, European Commission President Ursula von der Leyen had said that the bill was "by its very nature a breach of the obligation of good faith laid down by the withdrawal agreement."

The infringement process can ultimately result in the top EU court imposing sanctions, but this process takes at least several months.

A result can only be expected after Britain's transition period runs out at the end of the year.