Came back to this thread to find all the replies.
Some added information, it was a european airline, but not a British one, not sure if I'm allowed to state which one on here. We were flying from spain to London Heathrow, I don't know where British airspace starts and obviously as a passenger don't know where we are anyway but there was someone in the cockpit for the landing at Heathrow so that would definitely be British airspace and there was someone in there as we started descent so I'd guess that was in British airspace too.
The ages of the 2 different people were estimated to be between 16 and 18.
As a passenger if you see this sort of thing going on who and how do you report to the relevant person/body what has happened on a flight, obviously after landing at your destination?