Originally Posted by
KARFA
The only fast track lane you would encounter would be the security lane in flight connections at T3, and you could get it by status or cabin. I don't think there is anything you could get from the crew.
You won't need to go through to immigration on your connection as long as you take the airside connection route. There is more information which may be of help in the connection guide linked to in my signature.
On this route, doing the transit landside -- which means clearing UK immigration/passport control (and even customs, unlikely as that is to have an impact given arrival from an EU airport) -- is a recipe for missing connecting flights that are already cutting it rather close to the MCT for T5-T3 transfers.
Does the T3 flight connections security currently have a fast track security screening lane like it does for those originating trips landside at LHR T3? I know that there have been times when I've seen no such signs when doing T3 flight connections screening after coming in from flights that brought me into T5. Perhaps I wasn't looking closely enough there sometimes.