I've got absolutely no idea what either the aircraft or reasons involved were. However, I do know that there is at least one company in the UK contracted to fly as 'targets' for various missions by the military. They fly KingAirs (a big small aircraft if you see what I mean, twin prop-engined and high-tailed) and Dassault Falcons (also two engines but jets this time). Could your colleages have seen one of those along with a Tornado customer?