It seems most likely he carelessly fumbled selecting 7000, failed to check it and then wasn't talking to anyone (with radar perhaps) on the radio...silly boy.
I assume it was before the crabs made their heroic save-the-nation dash that London Centre were calling him vainly on Guard but naturally he wasn't listening to that either, they somehow knew his registration at that point (I was over France and could only hear the London side of the conversation) and were in contact with another aircraft that could see him but was not close enough to confirm his reg.
What a storm in a teacup, panic reacting as though a poxy little Gazelle near Ha'penny Green could be a threat to national security. We really have lost the plot, haven't we, crapping ourselves like a neurotic geriatric spotting a harmless hoodie at the other end of the park.?
