Ever since the Guardian revealed last month that Peter Mandelson was given security clearance against the advice of the UK government’s vetting agency, one question has dominated in Westminster. What were the concerns that led United Kingdom Security Vetting (UKSV) to tell the Foreign Office that his clearance should be denied in late January 2025, weeks before he was due to take up his post as ambassador to Washington? On Wednesday, the Guardian revealed several areas that multiple sources say contributed to that decision. UKSV identified concerns about associations Mandelson…