He said: “The Prime Minister and I had an excellent discussion and I’m very grateful to her for her restatement of the commitment to the very strong transatlantic partnership.
“We talked particularly about efforts to try to deal with counter-terrorism, the importance of our co-operation continuing.
“We also talked about Ukraine and Syria in particular.
“Most importantly we affirmed the imperative for the United States, Great Britain and the European community to work together to maximise the economic opportunity, minimise the disruption, deal with this in a way that has the wellbeing of the citizens of all of our countries and regions in mind in order to move our economies as fast as possible.
“I think the Prime Minister is very much committed to finding a calm, thoughtful, reasonable way forward that meets those needs.
“So I was encouraged by it and I look forward to conveying her very best wishes to the American people and President Obama.”