Was full due process followed in Lord Mandelson's vetting and appointment?

The Foreign Office granted Lord Mandelson security clearance despite advice from UKSV to undertake vetting, as confirmed by documents and a senior official's evidence. Sir Keir Starmer stated in Parliament that full due process was followed, unaware of the override at the time. Sir Olly Robbins was sacked as Foreign Office top civil servant after the clearance decision emerged.