PM says it is ‘staggering’ and ‘unforgivable’ that he was not told Mandelson had failed security vetting. Lucy Hough speaks to the Guardian’s head of investigations, Paul Lewis

Guardian investigation uncovers decision by UK security officials to deny clearance before Mandelson took up role as US ambassador

A decision to go against the recommendation of the vetting agency was taken by officials in the Foreign Office, spokesperson says.