Sir Keir Starmer is under immense pressure over his leadership of Labour after his party suffered devastating electoral losses across the country. Growing numbers of the prime minister’s own MPs, including some former loyalists , have called for him to go. Speculation over a leadership challenge had been growing for months before Thursday’s elections, with Andy Burnham, Angela Rayner and Wes Streeting all named as potential successors. But on Saturday, it was a more obscure backbencher who issued an ultimatum for the cabinet to put an end to Sir Keir’s premiership. Labour MP Catherine West told the cabinet that if they do not put someone forward to challenge Sir Keir by Monday, she will attempt to trigger a leadership contest herself. The prime minister has insisted he will not quit, and cabinet minister Bridget Phillipson insisted on Sunday that Ms West was wrong as she continued to back Sir Keir.…