Other senior Conservative Eurosceptics are doubtful, however, that Lee Anderson's move will lead to more defections - with one telling Sky News he is "not part of the Tory tribe".

Rishi Sunak will call a snap general election if 10 Conservative MPs defect to Reform UK, a top Tory with close links to Downing Street has claimed.

The source of the claim, made to parliamentary colleagues after Lee Anderson's shock defection, is an influential party figure with impeccable connections.

The prime minister's threat emerged as he mingled with Conservative MPs at the 1922 Committee's spring reception after a half-hour meeting with the '22 executive.

Traditionally known as "the men in grey suits", the senior MPs who make up the 1922 Committee executive have the power to make or break prime ministers.

According to parliamentary folklore, they have in the past handed a failing party leader "a glass of whisky and a pearl-handled revolver in a darkened room".