51�Թ�

Worried MPs say the whips – those in charge of party discipline – had raised the concerns of many with Downing Street.

But the sirens should have wailed when more than 100 Labour MPs wrote to the government whips last month.

One of them told us: "People have crossed a line - this isn't some whips' letter where the names are never leaked."

"The whips are pushing very hard with MPs but it's not working," the Labour MP said.

He served as a justice minister from 2010 to 2012, in the whips' office when the Conservatives were in opposition and chaired the influential Foreign Affairs Committee.