Sir Keir Starmer’s former chief of staff Morgan McSweeney is set to appear before the Foreign Affairs Committee on Tuesday to face questions over the Lord Peter Mandelson vetting scandal. Mr McSweeney, widely regarded as a protege of Lord Mandelson, was considered the driving force behind his appointment to the role of US ambassador. His appearance follows that of former Foreign Office chief Sir Olly Robbins , who was sacked by the prime minister earlier this month after claiming that he had not told the PM about the details of the vetting decision. Mr McSweeney resigned as Sir Keir’s chief of staff in February after taking “full responsibility” for advising the prime minister to make the appointment. He is alleged to have had knowledge about Mr Mandelson's continued dealings with Jeffrey Epstein after the financier’s conviction for child sex offences.…