PM said he was ‘staggered’ not to have been told that Peter Mandelson had failed his security vetting before becoming ambassador to the US

• Keir Starmer faces ‘judgment day’

• Five unanswered questions

One the central characters in the latest uproar over the failure in Peter Mandelson’s vetting is Sir Olly Robbins, a former member of the Foreign Office who was forced to quit on Thursday after new revelations about the process were revealed by the Guardian.

With Robbins due to appear before a committee of senior MPs next week, new information about how the process failed is expected to emerge. But what do Robbins know, and how was such a colossal mistake allowed to happen?