There are many issues here.
2 Gp crews tending to report every TCAS event (RA and TA) as an airprox, with a little ACP evidence building on the side.
The Voyager crew's understanding of the UK FIS and, thus possibly, the classification of airspace in which they were flying at the time.
The slow compliance by aircrews to instructions by ATCOs to turn and descend has been a contributory factor in a number of miltary airprox in recent years - formation turns and descents in IMC I understand but not single aircraft; however large.
At 1658L during the week there should have been an ATC Supervisor maintaining oversight, rather than distracting an ATCO from their primary duty. Especially when you consider that there were 4 radar positions open alongside the visual control room, with unit workload described as high to medium; too many times in recent years this has been a factor in military airprox. There is also something left unsaid here; the Director was setting up the PAR and thus, at a rough guess, was going to conduct the PAR having just directed the aircraft. Who then was going to fulfill the Director's roles and responsibilities iaw MAA RA towards the IFR traffic on PAR whilst they were conducting the GCA?
This distraction then led to them not monitoring the aircraft and not providing TI. The ATCOs prime role is to prevent collisions between aircraft and they can't do this if they're not watching what's going on. The way's in which an ATCO may prevent collisions is by issuing collision avoidance advice and/or by providing traffic information in order for the crew to determine a suitable course of action. In this situation they were unable to do either.
Root cause analysis would look at why that ATCO was placed in that position at that time of day, with that traffic loading, without a dedicated supervisor.
As for the UKAB's finding of cause, it is, as usual, utter guff. It is not a cause of the airprox (ie how the incident occurred) but a statement about what happened. The sooner the UKAB get their act together, as they have been told for a number if years now) the better.