As an Indian and a person who's flown India-UK several times, recommendations are :
Choice # 1 : BA
, especially if ur'e flying F or J to BOM or DEL. Only 744s and great service/food most of the time.
Choices # 2 : EK
if you don't mind making a transit stop in DXB
or Bahrain. Great service in all classes and probably 15-20% cheaper than BA
(SriLankan) is also good LHR
-CMB but the connections to BOM and DEL from CMB are a little irritating in terms of timings, but UL
will probably throw in a free nite's stay in CMB which may be worth your while if you haven't seen the place yet.
Choice # 3 : Air India. Take a chance, you may be surprised, sometimes they do a good job. Food is normally good. However don't expect any fancy IFE systems in Y class.
Choice # 4 : Aeroflot. Via SVO
. Probably very cheap. Never flown Aeroflot myself but I hear they're "new and improved" nowadays. If you're flying to DEL it'll be a 777 or 767-300 but BOM will be a TU204.
Choice # 5 : SyrianAir. The cheapest. And probably the only chance for u to fly on a 747SP into Bombay.
Hope it helps!