British and EU negotiators have not yet reached a Brexit withdrawal agreement, despite a flurry of activity on Sunday that led to speculation a deal was at hand.

Brexit Secretary Dominic Raab dashed to Brussels earlier today in a surprise visit.

But Michel Barnier, the EU’s chief negotiator, said this evening that despite “intense efforts” some “key issues” remained unresolved.

And a spokesperson for Downing Street and the Brexit department said: “In the last few days UK and EU negotiators have made real progress in a number of key areas. However there remain a number of unresolved issues relating to the backstop.

“The UK is still committed to making progress at the October European Council.”

Ambassadors from the remaining 27 EU states were invited to attend an update on the talks in Brussels.

Any developments in the Brexit process will be closely scrutinised by Tory MPs, who fear that Theresa May will give away too much in the negotiations and potentially leave the UK indefinitely tied to the EU’s customs union.

The prime minister faces a potential resignations from her Cabinet and any deal could also have major repercussions for her pact with the Democratic Unionist Party.

Former Brexit secretary David Davis has urged a Cabinet revolt against the prime minister’s strategy.

The issue of the Northern Irish backstop – a mechanism to avoid a hard border – is at the heart of the troubles facing May’s leadership.

The EU’s version of the backstop, which would see just Northern Ireland remain aligned with Brussels’ rules, has been called unacceptable by May and is loathed by the DUP.