The next available flight that they could offer was six hours later. Unfortunately for me, this alternative was of no use at all as I could not make the appointment that I was flying to, so I decided not to go, and reschedule for another day.
I understood the semantic in the previous answer I gave.
I am just intrigued that BAA seemed to think it within their remit to hold me airside.
They didn't hold you, they delayed you. For obvious reasons (and if they are not obvious, I have no intention of discussing them publicly) you cannot pass through security into a restricted area, and then demand to be allowed to pass back from that area without following the appropriate procedures. Those procedures will depend on the nature of the reversal. For example an emergency, or a cancelled flight with or without baggage, international, domestic, common travel area, etc. The reason for reversal might be as in your case, elective. It might be denied boarding on the airlines part for whatever reason.
I can understand your frustration at it taking 90 minutes to get somebody to escort you back landside, and in regards to this complaint I wouldn't otherwise comment, however it isn't false imprisonment. The security staff would be absolutely correct in calling the Police if you refused to comply with the proper security procedures and it would be most unwise to argue the point unless you were absolutely sure of your assertion. To the poster who refers to these staff as "monkeys", they are individuals doing their job. However much you dislike that job, or anybody employed to do it, they are required to follow rules (even if they dislike those rules), or face dismissal.