flew to Brussels today in an effort to break the "deadlock" in the negotiations over Britain’s exit from the European Union.
The Prime Minister will meet the EU’s chief negotiator Michel Barnier and Commission President Jean-Claude Juncker just days after they raised serious concerns about the rate of progress in talks.
Downing Street sources insisted the meeting had "been in the diary for weeks" but the announcement caused surprise in Westminster.
It comes after last week's negotiations ended with little movement and Mr Barnier said there was a “disturbing deadlock”.
Mrs May, who will be joined by Brexit Secretary David Davis, is expected to have discussions with European counterparts over the coming days ahead of a meeting of all EU leaders later in the week.
No 10 said the PM and German chancellor Angela Merkel had agreed the "importance of continued constructive progress" in the UK's exit negotiations in an early morning telephone call on Sunday.
Over dinner, the PM will hope to end the stalemate over the divorce settlement that is stopping post-Brexit trading relationship being discussed.
Talks: Theresa May and Angela Merkel have discussed negotiations over the phone (Getty Images)
After the fifth round of discussions were brought to a close last week, Mr Barnier said he would not recommend that talks moved on to the next stage when he attends the European Council on Thursday.
He said the negotiations had ended without making any "great steps forward" and there was "disturbing deadlock" over the size of Britain's divorce bill.
Mr Juncker said the Brexit process will take "longer than we initially thought", blaming delays on Britain's failure to settle its financial obligations.
The Government wants EU leaders to expand Mr Barnier's negotiating mandate to allow some headway to be made.
Labour's John McDonnell suggested yesterday that Tory MPs are in talks with Labour to prevent Britain leaving the bloc without a deal.
The shadow chancellor said Parliament can stop the Government taking the country out of the block without an agreement in place and claimed discussions are "going right the way across the House".
But Chris Grayling said the Labour MP was talking "nonsense" and accused him of threatening to create a chaotic Brexit
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