Good stuff guys but just remember that we usually only "Flight Check" (calibrate) Glideslopes to 10nm from touchdown....can't remember if LHR is a Calibrated to longer range, i'll check when i get a chance.
We had a situation a while ago at a major UK airport where controllers were routinely vectoring onto the glide at around 14 miles....It's now a requirement for us to check that one out to 15.
Unfortunately just because it's ok at 10 doesn't mean it will be at longer range...i've seen all sorts of weird things out there!
Cheers