Work and Pensions Secretary Amber Rudd has quit the Cabinet and Conservative Party saying she cannot “stand by” while “loyal moderate Conservatives are expelled”.

Such a high profile resignation from his heart of his cabinet will come as a huge blow to Mr Johnson, who has been fighting a rearguard action since MPs took control of the Commons this week to force him to seek an extension to Brexit on October 31.

In her letter to Mr Johnson, Ms Rudd said that the expulsion of 21 Tory MPs last week was an act of “political vandalism” that was also “an assault on decency and democracy”.

The MPs — including various former cabinet ministers such as Ken Clarke — were forced out of the party after they voted with opposition MPs to block a no-deal Brexit.

“This short sighted culling of my colleagues has stripped the party of broad-minded and dedicated Conservative MPs,” she wrote in her letter to the prime minister. “I cannot support this act of political vandalism.”