Whilst I might be minded to agree with you, as I stated in my OP this happened at LHR...where the staff turnover is low, and I fly through there regularly (and know quite a few people there).
Not to go into major details of what happened, but the agent questioning me (who took over from the first agent after 2 questions) didn't seem to like me, and had a major chip on her shoulder (which became more obvious with a run-in at the gate with her).