Since there are still some questions about the terminals in LHR, I have created a list of which airline goes to which terminal.
I can imagine that the list can vary daily (I am 100% sure that all American airlines were still on T2 last year.), the data was as of February 26th. taken from this, perhaps not all airlines that can be found in my other list land there.
Aegean Airlines – T2
Aer Lingus – T2
Aeromexico – T3
Air Algerie – T4
Air Astana – T4
Air Canada – T2
Air China – T2
Air France – T4
Air India – T2
Air Malta – T4
Air Serbia – T4
American Airlines – T3
ANA – T2
Asiana Airlines – T2
Austrian – T2
Avianca – T2
Azerbaijan Airlines – T4
Bejing Capital Airlines – T3
Biman – T4
British Airways – T5 (BIA, BLL, OTP, GIB, GOT, OSL, PRN, PUY, TIA, VIE @ T3)
Brussels – T2
Bulgaria Air – T4
Cathay Pacific – T3
China Airlines – T3
China Eastern – T4
China Southern – T4
Croatia Airlines – T2
Delta Air Lines – T3
Egyptair – T2
El Al – T4
Emirates – T3
Ethiopian Airlines – T2
Etihad Airways – T4
Eurowings – T2
EVA Air – T2
Finnair – T3
Gulf Air – T4
Hainan Airlines – T3
Iberia – T5
Icelandair – T2
Iran Air – T3
ITA Airways – T4
Japan Airlines – T3
Kenya Airways – T4
KLM – T4
Korean Air – T4
Kuwait Airways – T4
LATAM – T3
Loganair – T2
LOT – T2
Lufthansa – T2
Malaysia Airlines – T4
MEA – T3
Oman Air – T4
Qantas – T3
Qatar Airways – T4
Royal Air Maroc – T4
Royal Burnei Airlines – T4
Royal Jordanien – T3
RwandAir – T3
SAS – T2
Saudia – T4
Shenzen Airlines – T2
Singapore Airlines – T2
Sri Lankan Airlines – T3
Swiss – T2
TAP – T2
Tarom – T4
Thai Airways – T2
Tianjin Airlines – T3
Tunisair – T4
Turkish Airlines – T2
Turkmenistan Airlines – T4
United Airlines – T2
Uzbekistan Airways – T4
Vietnam Airlines – T4
Virgin Atlantic – T3
Vistara – T3
Westjet – T4