Although it is not 100% clear from the plans, I count about 44 gates (with jetways) at Terminal 5. Given that T4 is 26 gates, and given the large BA prescence at T1, will BA actually fit 100% into T5?
It seems to me they might need to keep Domestic flights in T1 which would be practically the same inconvenient way it works now changing at LHR onto a BA longhaul flight.