Yes, Terminal 3 !

Not all BA flights leave from T5!

Until now, flights departing from Terminal 3 needed a bus to ferry travelers from the terminal to the aircraft.

This has meant lengthier boarding time and earlier gate closures too.

This was always a pain. I always thought it to be expected of a budget carrier such as Ryanair but not of British Airways.

Over 95% of British Airways flights will now have direct pier-walkway connections

This is possible due to airlines moving to the new Terminal 2 from Terminal 3

According to the Heathrow Departures Board, BA flights leaving from terminal 3 include the following destinations:

Prague
Lisbon
Vienna
Budapest
Warsaw

Plus of course, codeshare flights (flight numbers prefixed with BA) where Finnair (Helsinki), American Airlines (to New York, Dallas etc.) and Japan Airlines etc. are the operating airlines.