Theresa May is facing an autumn ambush to try to force Britain to accept freedom of movement after Brexit as a menacing cabinet split opens up over immigration.

A European ambassador has warned the government that the EU negotiator, Michel Barnier, will put freedom of movement back on the table at May’s moment of maximum weakness ahead of the Conservative Party conference.

Senior government officials say they expect the EU to demand continued freedom of movement if Britain wants frictionless trade in goods with the EU, but May’s team is divided over how to respond.

Sajid Javid, the new home secretary, has torn up plans to offer European migrants preferential access to Britain after Brexit.

It has put him at odds with the Treasury and