Oneworld
Due to the construction of Terminal 5, most British Airways flights moved out of Terminal 1 to Terminal 5 during 2008. The remaining British Airways flights moved to Terminal 3 on 25 February 2009, later than originally planned. Finnair, a member of the oneworld alliance, moved to Terminal 3 in January 2009, to join other oneworld carriers.
Since the buyout of British Midland International, British Airways service some Short-Haul and Medium-Haul destinations from this terminal, marking its return to the terminal since it moved out in 2008
Read more about this topic: London Heathrow Terminal 1, Terminal Reorganisation