DL26, I couldn't concurr more. The length of the acft turnround has little relevance to the time the security require to do their job properly. You can have a 3 hr check in if that's what is req'd from a security point of view, but that should not affect the turnround time of the acft.
Trouble is, ground staff then inflict their problems onto the departing flight. Try getting sense out of LHR staff!