Not sure of the exact numbers, but in terms of the BA-liveried aircraft, all of CityFlyer's RJ100's moved to the regions after the integration of the company. Routes were either dropped or transferred onto the BA 737 fleet.
Separately, GB Airways have transitioned from a 737 fleet to an A320/321 fleet.
easyJet also have moved from being a 737 base to an Airbus A319 base (though still with a few 737 movements?).
If you add the sizeable easyJet and GB Airways number of movements, let alone the multiple other Airbus operators, there is a very high proportion of LGW short-haul on the A319/320/321.