Recently flew from Cairo, and in order to get through security before check-in, I had to tick my own name off on a print out of the manifest (which oddly grouped names by the first letter of the surname, but not in an alphanetical list - The "E's" were almost at the bottom of the list for some reason).

What I would suggest is asking the check-in agent at LHR for an e-ticket receipt which will be printed on normal ticket stock. This should avoid any problems on the return as security will see it as a ticket.

Hope this helps.