Mrs May, who met Mr Tusk in London earlier this month, has not yet said publicly when she will formally notify the EU of Britain’s intention to leave, revealing thus far only that she would not trigger the talks before the end of this year.

Mr Tusk was speaking at the end of an emergency EU “unity” Summit in Bratislava that ended in disarray when the Italian prime minister refused to share a stage with his French and German counterparts and the Hungarian prime minister blasted Germany over its "naive" migration policy.

Matteo Renzi, the Italian prime minister, said he could not be part of the joint press conference because of disagreements over the economy and immigration.

He said Europe must abandon austerity and that, when it comes to the trade surplus: "Germany does not respect the rules," according to La Repubblica.