Sir Keir Starmer has accused the Foreign Office of covering up the scandal over Lord Mandelson’s failed vetting.

The Prime Minister said officials had made a “deliberate decision” to withhold the fact that the disgraced peer had failed security checks before being appointed ambassador to the US.

He has denied failing to ask the correct questions about Lord Mandelson’s security clearance during the appointment process, as well as after the peer had been sacked.

The Prime Minister said: “If I had been told that Peter Mandelson or anybody else had not been given clearance on security vetting, I would not have appointed them.

“A deliberate decision was taken to withhold that material. This was not a lack of asking. This wasn’t an oversight. It was a decision taken not to share that information,” he added.

Sir Keir said it was “unforgivable” that Foreign Office officials had asked Yvette Cooper, the Foreign Secretary, to sign a statement last year claiming that Lord Mandelson had passed vetting