Keir Starmer says it is ‘staggering’ and ‘unforgivable’ that he was not told Peter Mandelson had failed security vetting before taking up the role of US ambassador. The comments follow a Guardian investigation that exclusively revealed Mandelson had initially been denied clearance after a background check by security officials, but that the decision was overruled by the Foreign Office. Lucy Hough speaks to the Guardian’s head of investigations, Paul Lewis – watch on YouTube