The Conservative Party "will not be trusted for a generation" if Theresa May "fudges" Brexit, senior activists have warned.

In a letter to the Telegraph, grassroots Tories said the Prime Minister would be "playing with fire" if she brings forward plans for Britain's departure from the European Union that "frustrate the will of the people".

The intervention comes after David Davis, the Brexit Secretary, and five other members of Mrs May's 11-strong Cabinet sub-committee on Brexit opposed her plans for a new customs deal with the EU.

Mrs May has now ordered two groups, one including Mr Davis and Karen Bradley, the Northern Ireland Secretary, and the other bringing together David Lidington, her pro-Remain de facto deputy, and Michael Gove, the Environment Secretary, to attempt to solve the problems around her favoured proposals, and a second option backed by Brexiteers, in an attempt to form a consensus around one plan.

In the letter, whose signatories include Ed Costelloe, the chairman of the Grassroots Conservatives group, the activists also raise concerns about recent votes in the House of Lords to hand power over the negotiations to Parliament, and to keep Britain in the EU's single market after Brexit.

They state: "The local election results show that the Government is being supported to deliver a sensible, non-fudged Brexit.