EU warns London over undermining Brexit agreement

But the British government responded that it would only mean "minor clarifications in extremely specific areas".

"I trust the British government to implement the Withdrawal Agreement, an obligation under international law and a prerequisite for any future partnership," von der Leyen tweeted on Monday.

"Protocol on Ireland/Northern Ireland is essential to protect peace and stability on the island and integrity of the single market," she added.

In London, a government spokesperson said that the UK was still committed to implementing the withdrawal agreement and the Northern Irish Protocol - which prevents a hard land border between the Republic of Ireland and Northern Ireland, ensuring the well-functioning of the EU's single market.

"We are taking limited and reasonable steps to clarify specific elements of the Northern Ireland protocol in domestic law to remove any ambiguity and to ensure the government is always able to deliver on its commitments to the people of Northern Ireland," he said.

Despite having formally left the bloc last January, the UK remains in the so-called transition period until the end of 2020, as both parts try to secure a post-Brexit trade agreement with no tariffs and quotas.

October surprise

However, the UK's prime minister Boris Johnson on Monday set 15 October as the cut-off date to reach a post-Brexit trade agreement, saying that there is no sense in thinking about timelines beyond this date.

"If we can't agree by then, then I do not see that there will be a free trade agreement between us," he said, according to a statement released by its office.

Ahead of the eight-round of negations, which begins on Tuesday in London, the European Union's chief Brexit negotiator Michel Barnier expressed his concerns about the upcoming talks - which have been mainly focussed on clashes over state-aid rules and fishing quotas.

"I remain worried," Barnier told French radio on Monday, adding that "the British would like the best of both worlds - export their products to the European market on their terms".

'Backmail'

Meanwhile, the European Parliament's trade committee chief, MEP Bernd Lange, said that he was "shocked" by the way UK counterparts are negotiating.

"I haven't seen anything like it in decades. We will not allow ourselves to be blackmailed. We stick to agreements," he said in a statement.

"What madness to believe today that one can achieve actual sovereignty in complete independence. The British illusion of sovereignty will lead to the greatest loss of sovereignty in British history," he added.

For his part, the president of the European Council, Charles Michel, referred to the issue as an ongoing battle to defend the EU's interests.

"We might be losing the UK, but we won't lose our stiff upper lip," he said.