This is why I avoid T5 (and BA from destinations where they only offer LHR flights). It's crazy - it takes me 2:30 hours to fly across the Europe and then I'm stuck at LHR during one more hour (exact time it took me from gate to Heathrow Express station last time).
It went that far that I actually prefer EasyJet on VIE-LON route (VIE is my home airport).
Since I'm 18 now I may give LHR another try with e-passport gates, but it's funny that they don't allow it to 17y old since officer won't ask you any age-related additional questions anyway.
By the way, any idea why is UK probably the only EU country that scans EU passports on arrival? I actually found out that it's faster to use National ID (which they apparently can't scan) than passport.