Ever since BA took over bmi 18 months ago, it has found itself returned to a situation it was in three years ago at London Heathrow. That is operating across three terminals in the airport (1, 3 and 5).
This is plainly undesirable from the perspective of both passenger experience and efficiency. Terminal 1 is unpopular for many reasons, not least the general condition of the terminal which is due to close in 2016.
BA has now confirmed that it will consolidate its operations in Terminals 3 and 5 from 2015. The new Terminal 2 will not be used by any Oneworld carriers.
I would not take this as read as the existing Terminal 1 routes (Amman, Beirut, Belfast City, Cairo, Dublin, Hanover, Luxembourg, Lyon, Marseille, and Rotterdam) will necessarily move into Terminal 3.
BA has indicated that the consolidation of operations into two terminals will result in changes to both the aircraft assigned to routes (the Terminal 1 operation uses Airbus A319 aircraft and A321 aircraft configured in a long-haul configuration) and which routes operate outside of Terminal 5, which is the preferred terminal for routes.
By extension, this means that there may be some significant moves of current routes out of Terminal 5 into Terminal 3.
You can check which terminal your BA flight is currently operating out of on ba.com