I have to mention that on a recent experience with LHR, I was quite dissatisfied with the security personnel at T5 who I thought were both rude and arrogant. First, as an EXP, I thought we were allowed to utilize the fast track line at T5 (came in on an AA flight TATL in J, transferred onto a domestic UK flight with BA with no CE). The BA gatekeepers on the lower level allowed me into the fast track lane, but when I got upstairs, the security personnel informed me that since I am not traveling in J or F, that I am not allowed to use the fast track lane and tried to send me to one of the other lanes. I informed them that I was an EXP and arriving on a J ticket and transferring to Y since there was no J on this UK domestic flight; and in the process was accused of being "arrogant". Obviously, I was quite irrate at that point, spoke with the supervisor for this agent, and got his name and badge number to file a complaint with BA/BAA. Nevertheless, this has been only one poor security experience in over 10+ years of transiting in LHR.