Mr Wakeford’s defection is the culmination of months of work by Labour figures, codenamed “Operation Domino”, to entice him to Sir Keir Starmer’s benches.

On Wednesday night, friends said his decision had “not come as a surprise” because he was politically “closer to Keir than to Boris”.

Labour sources said other Tory MPs from the 2019 intake could follow Mr Wakeford out of the door, with one MP suggesting that as many as five were considering leaving their party.

“I have been speaking to other friends across the floor who are incredibly disillusioned and are feeling more and more like their future would be under a Keir Starmer government than a Boris Johnson one,” the MP said.

Another Labour source said they had personally spoken to three Conservative MPs who had expressed doubts about their future in the party.

Mr Wakeford is understood to have been “coached” by Chris Elmore, the Labour MP for Ogmore, for around six months over the decision. On Wednesday, Mr Elmore walked with him into Prime Minister’s Questions, where he took his seat on the Labour benches for the first time.

The decision was announced just minutes earlier, as Mr Johnson got into his car in Downing Street to travel to Parliament.

Several shadow cabinet ministers learned of the defection only half an hour before it took place, with one party adviser describing it as a “proper secret squirrel operation”.