Theresa May has categorically ruled out keeping Britain in any form of customs union with the EU in a significant victory for Brexiteers ahead of two crucial Cabinet meetings this week.

Downing Street said it wanted to “put to rest” arguments that have raged for weeks about whether the UK would join a customs union after Brexit.

Following reports that Eurosceptic Tory MPs were plotting a coup if Mrs May bowed to the will of Remainers, sources close to the Prime Minister insisted customs union membership was off the table.

A No 10 source said: “We must be free to sign trade deals with the rest of the world...so it is not our policy stay in the Customs Union. It is not our policy to stay in a customs union.”

It represents a significant change in stance from Mrs May, who as recently as Friday refused to rule out being part of a customs union.