Brexit negotiations have not begun promisingly and Cabinet divisions mean it is hard for the Government to have a clear position, a former head of the diplomatic service has said.

Sir Simon Fraser, who was the chief mandarin at the Foreign Office until 2015, said the UK side had been "a bit absent" from the formal negotiations in Brussels.

He said transitional arrangements covering the period after the UK leaves the European Union in March 2019 would be vital because there is "no way" that a deal on the future relationship with the bloc will have been finalised by then.

Sir Simon, who now advises businesses on Brexit and foreign policy, said: "The negotiations have only just begun, I don't think they have begun particularly promisingly, frankly, on the British side.

"We haven't put forward a lot because, as we know, there are differences within the Cabinet about the sort of Brexit that we are heading for and until those differences are further resolved I think it's very difficult for us to have a clear position."

The Government is reportedly set to publish further "position papers" setting out its views on customs arrangements and the Northern Irish border in the coming weeks, and Sir Simon said that would help demonstrate the UK team led by David Davis is "ready to engage".