A former head of the Secret Intelligence Service MI6 has told GB News that he “cannot believe” that the Foreign Secretary was not informed that Peter Mandelson had failed security vetting.

Sir Richard Dearlove said: “The problem ultimately is caused by the Prime Minister choosing an ambassador with a known integrity problem. Everybody understood that about Peter Mandelson, if you look at his past record.

“I’m not criticising his abilities, but as the talisman for New Labour, he had a very dodgy series of relationships. We won’t go into that. So there should have been, the Prime Minister should have thought through before announcing the appointment how he was going to manage that aspect of choosing Mandelson.

“But let me just move on now to the whole process of the DV. I cannot believe that a Permanent-Under Secretary, when he got the results of the DV, didn’t ring up his minister, who he talks to every day, and say to him, ‘Look, Mr Lammy, minister, we have a problem, and we have to work out now how we’re going to manage that problem’.

“Did Olly Robbins really take it on himself to not tell anybody and decide, as the Permanent Under-Secretary of the Foreign Office, that the risk was manageable? I mean, whichever way you look at it, it’s a mess. It was a bad choice in the first place. It was an appalling choice in the first place.

“I said this on the very day the appointment was announced, and I said this is going to cause the government probably massive problems. So whichever perspective you take, it’s really damaging because it’s either a question of judgement or a failure of process, one or the other.”

He added: “There is confusion about the results of a vetting process. You do not divulge the detail of the vetting process. You can’t explain the detail. It’s all high confidentiality, but the results of the vetting process without explanation are significant.

“I just cannot believe that a Permanent Under-Secretary as experienced and able as Olly Robbins didn’t actually say to Lammy, his minister, because that would be the first point at which you’d discuss it: ‘Look, he’s failed. What are we going to do now?’ Lammy could have said, ‘Okay, we can manage the risk. I’ll inform the Prime Minister.”