As I mentioned in another thread (https://www.flyertalk.com/forum/35062119-post64.html) it is currently a 50-50 split between T3 and T4 of the SkyTeam members at LHR. If I recall correctly, before the T4 closure and terminal musical-chairs during 2020/21, only DL, ME and GA (before GA ceased LHR flights, I flew on a few times from T3) that were T3 residents and all the others were at T4, along the with the SkyTeam lounge (opposite Gate 10) - which is now (unfortunately) permanently closed.