I have no idea where a BERGI dep from EHAM will take you, but seeing as I am not familiar, it is probably to the East. Anyway, that is largely irrelevant. Most probably *US, almost certainly a tanker & chick. It is common practice for fast jet fighter/bomber re-positioning on a long trip (for many reasons, including: Aircraft delivery, Tech replacement, routine rotation, exercise deployment/recovery, etc..., etc...) to travel under-the-wing of a tanker. Such flights may & are conducted, with utmost safety, along the same air routes as used by passenger carrying air transport aircraft. They are treated as, and obey the same rules as, any airliner. A novelty factor for 'those passengers on the left side of the aircraft....', but otherwise, a routine event, neither escort nor intercept.
For the morbid, or any journos reading, the only 'event' in UK airspace yesterday (11/9) was a BE20, en-route Scotland to London early that morning, who suffered a 'radio failure' near Leeds. Sphincters twitched, only very slightly, before a genuine RT fail was confirmed and a hi-jack situation eliminated. A non-event.
Rgds,
Hippy.
*'Most probably US' because, from evidence:
a) Being high level near Amsterdam, Westbound, were obviously en-route to UK, CAN or USA.
b) UK will usually use 3 engined jet for long-range tanking (L101). We have 4 engined tanker (VC10), but they have pairs of engines that would 'appear' as a 'two engined' aircraft from viewing contrails at that distance.
c) US routinely use 4 engined KC135 on that route.
d) CAN had no notified activity in that area.
e) Could quite easily have been the French KC135 & MIR reported, I can neither confirm nor deny, but sounds like a plausible routine event.