THERESA May will dine in Brussels on Monday with European Commission president Jean Claude Juncker and his chief negotiator Michel Barnier in a bid to break Brexit deadlock ahead of this week's crucial EU summit.
No10 sources said last night the unusual move – which has raised eyebrows – was long planned.
But prime ministers usually only travel to meet heads of state.
It followed a tense phone call yesterday afternoon with the German Chancellor Angela Merkel.
Mrs May was bidding to try and break the current impasse after Germany and France took a harder line than other countries and rejected proposed transitional arrangements.
Paris and Berlin want Britain's divorce bill settled before they move onto a transitional deal and trade talks.