A few updates from me:

STN and GLA remain as in the guide. Only one scanner at each. STN is easily avoidable. GLA also, but it appears they close most of the other lanes in the evening.

LHR T3 now has at least three scanners, from my vantage point. There may have been more, but I didn't see down the entire hall. They are only used as secondary on those who beep the WTMD. When I was there, each pair of open X-Ray belts has one WTMD and one body scanner. The closed belts had lanes without body scanners. The WTMD was doing a different beep (presumably "random" selection) every three or four people, so high chances of being asked to use the NoS, but easy to guess when to walk through to avoid the "random" beep.