Also worth noting is that the Flagship Lounge in T3 is just seconds from the boarding areas for gates K12-20. There is even a back door from the lounge that opens directly into the boarding area for one of the gates (I can't remember for sure which gate that is right now, but I think it's K18). On several occasions, I've remained in the lounge right up to the moment boarding begins for the evening flights to LHR and then just gone directly from comfy lounge to comfy C or F seat. Very nice.