Theresa May will face a coup that would install a “dream team” of “three Brexiteers” if she persists with plans to keep Britain in a customs union with the European Union, Tory MPs warned last night.

Eurosceptics contacted Boris Johnson, the foreign secretary, on Friday and urged him to agree a pact that would see Michael Gove, the environment secretary, become his deputy prime minister and Jacob Rees-Mogg — the shop steward of the backbench Brexiteers — appointed chancellor if the prime minister is forced out.

While encouraging MPs to “rally round” May, Johnson also told one of the plotters that he would be “ready” for a future contest. He vowed that the “cavalry is coming” to block the customs union plan when May’s Brexit