David Davis could walk out on his job as Britain’s lead negotiator on Brexit because of frustrations that he is being cut out of key strategic talks in Whitehall, his friends fear.

Allies of the Exiting the European Union secretary said they were concerned he is not being included by civil servants in key talks about Britain’s negotiations about leaving the European Union.

One source said that Mr Davis had not been shown a key Brexit Cabinet paper sent by Boris Johnson, the Foreign secretary, and Michael Gove, to the Prime Minister.

The fear is that Mr Davis might resign in protest – in the same way that he suddenly quit as shadow home secretary from David Cameron’s front bench team in 2008.

Mr Davis has been been a vocal exponent of the Government’s Brexit policy, making two speeches this week and a third on Britain’s trade deal with the EU after Brext next week.

Allies of Mr Davis, who is known as "DD", said Mrs May had been 'captured' by civil servants Sir Jeremy Heywood, the Cabinet secretary, and Oliver Robbins, the former DExEU permanent secretary, who now works in 10 Downing Street advising Mrs May.