BA have always planned to maintain services in T3 for a number of reasons. The main one being that even with a capacity of 30million a year, T5 could never accommodate all BA LHR operations. Also, T3 allows BA and other OW carriers to work better with codeshare and JSA routes (HEL, Spain and Aus routes). T3 also allows BA room for expansion when the time comes, without having to go back and fight to get room in another terminal when more space is needed. BA will have both check-in and lounge space in T3. Terminal allocation at LHR is all about politics. Being in a particular terminal means you have a say on how things go and can keep an eye on the competition. That's one of the main reasons BA had the Miami flights from T3. Also by having the Miami flights in T3, it made it easier for BA to secure T3 as the additional base along with other OW carriers with the terminal changes now in progress.

Rambuster, the T3 lounges are being developed to the same standard at the T5 lounges. The aim is to make the T3 experience as close as possible to the T5 experience.