Airtanker 'own' 14 A330 Voyager jets, 9 of which are in the RAF 'core' fleet, and 5 are retained by Airtanker in the 'surge' fleet.
All but one of the 9 aircraft RAF core fleet are painted in RAF grey, and wear RAF roundals, serials and titles. The one exception is ZZ336, which was painted in a mostly white scheme a few years ago. It operates as BoJo1, and flies the PM on long distance foreign travel. ZZ336 is often used in photo opportunities. However, it can also be used as a normal transport/tanker, and indeed it often operates as the nations QRA tanker since it is usually at Brize waiting for the next PM trip, whereas the grey fleet is off around the world doing transport stuff.
The 5 aircraft 'surge' fleet are retained by Airtanker. The intention is/was to lease these aircraft out on the civil market to reduce costs. In an emergency, the RAF can then 'requisition' these aircraft back into service. In the recent past, some of these jets have been leased to Thomas Cook and Condor, and when in service with those airlines they are painted in the colours of those airlines. Therefore, you may well have flown on an RAF Voyager without realising it. Two of the surge aircraft are used by Airtanker (in RAF grey but with Airtanker civil markings) to operate the Falklands air bridge - two return flights a week. There are fewer diplomatic issues operating 'civil' aircraft to/from the Falklands than there are operating military ones
- particularly now the runway at Ascension is FUBAR.
You should also note that SOP for a 'live' QRA intercept is not to fly the two fighters off each side of the intruder. One fighter will fly alongside to make it's presence known to the cockpit crew and provide visual instructions and identification. The second fighter will trail the intruder by a mile or two incase the intruder does not follow the instructions given to it by ATC or the first fighter, and "enforcement" action is needed. So if you see an 'airliner' in formation with 2 or more fighters then it's a fly-past. If it's an airliner with a fighter a mile or two behind, then it's probably not a fly-past.