Allegations that Peter Mandelson leaked Downing Street emails and market-sensitive information to Epstein, a convicted sex offender, following the financial crash, have now led to a criminal investigation. Wednesday’s events in the House of Commons showed that they have also unleashed a Westminster scandal which threatens to engulf Sir Keir Starmer’s premiership. The prime minister’s political future may rest on his ability to convince MPs that he is being transparent over the fateful decision to make Peter Mandelson the UK’s ambassador in Washington.