LHR - NoS at all terminals (T1 MMW, T5 BKSX, other terminals unknown), random selection (based on who is passing by when the machine is free), no opt-out. Transit checkpoints are safe, as is T1 Zone K.
T5 does not have backscatter, hasn't for a long time. It used to have MMW at North, Cancerbox at south. The cancerbox has been fully removed, and I think the MMW has too.