Deputy prime minister says it is ‘inexplicable’ top civil servant kept Downing Street in dark

Keir Starmer would have blocked Peter Mandelson from serving as the UK’s ambassador to Washington had he known he failed security vetting, David Lammy has said, as he attempted to shore up the prime minister amid damaging fallout from the row.

In his first public comments on the vetting affair, Lammy said it was “inexplicable” that Oliver Robbins, the former top civil servant who was forced out of the Foreign Office this week, had opted to leave Downing Street in the dark over the outcome.

Starmer has been under intense pressure since the Guardian revealed on Thursday that the Foreign Office had overruled a decision to deny Mandelson security vetting clearance. He will face MPs on Monday as he attempts to limit the damage to his premiership.

Lammy, the deputy prime minister, told the Guardian he had been “shocked and surprised” when he had first learned last week what had happened.