Sir Keir Starmer will face mutinous Labour MPs as he fights for his political survival after the resignation of his top aide over the Lord Peter Mandelson scandal.The Prime Minister is on Monday expected to address a meeting of the Parliamentary Labour Party (PLP) amid anger over his appointment of the peer as ambassador to the US despite knowing that his links with Jeffrey Epstein continued after the financier’s conviction for child sex offences.It comes a day after Morgan McSweeney quit as Sir Keir’s chief of staff, taking 'full responsibility' for giving the Prime Minister advice that resulted in the 'wrong' appointment.But scrutiny of Sir Keir’s own judgment is mounting as critics, including some of his MPs, have highlighted that he made the final decision.The pressure on his premiership looks unlikely to ease as the Government prepares for the lengthy process of releasing tens of thousands of emails, messages and documents relating to Lord Mandelson’s appointment.Sir Keir believes the files will prove the former Labour grandee lied about the extent of his ties to the notorious paedophile during his vetting.