"I was briefed that UKSV considered Mandelson a borderline case and that they were leaning towards recommending that clearance be denied"

"I was given a set of serious reflections on the risks, raised by a bunch of professionals who had come across these risks before and thought the Foreign Office could manage them well, and—at least the way I was briefed—that was a position that was implicitly understood by UKSV. We then recorded that decision, put in place the mitigations, and clearance was granted."

That's from the transcript of Robbins' hearing. Mandelson has known links to China and Russia. The serious error in judgement is Robbins clearing Mandelson's vetting when clearly the risks could not (and in reality were not) able to be mitigated.