Originally Posted by
GUWonder
LHR indeed does sometimes have something approaching what appears to be exit passport control checks. It's not common and it's not a daily procedure like in the US or say the EU Schengen countries, but such checking of passports of persons departing the UK from LHR indeed does sometimes exist where you noted above.
I can't find anything concrete in this regard but IIRC it was a pledge of both parties in the UK coalition government to re-introduce exit checks (in spite of the fact that it was the last Conservative administration that did away with them!).
Confirm that on a recent flight out of STN there were UKBA staff checking documents (not everyone's though) just before the exit from the security zone.