Aussiestu - I must agree that my first reply was slightly daft! I'll explain the rationale behind my initial replies.
Having looked at an aerial map of LHR, I would imagine that major amendments will be made to the Bravo cul-de-sac (?) if BA were to expand in T1. [Has anyone got specific details?]
My surprise comes from the fact, as Mrjworth hints at above, T1 as it stands, hasn't really got the floor-space/facilities to cater for B747/B777 passenger numbers and any changes would necessiate major construction works. This isn't to say it "won't happen" but I was under the impression that, in the short to medium term, BA were hell-bent on T5 so that they could merge short & long haul ops under one roof, so this "latest news" doesn't fit that well with BA objectives.
Also, wouldn't a long-haul split between T1 and T4 complicate BA ground ops even further? I know several long-haul flights operate out of T3, but a move to T1 means transferring support staff and equipment back from T4 to T1! Not exactly a cheap operation and loss of economies of scale. I hasten to add I could be very wrong!
Note to Ikraus; BA does operate B767's out of T1 already, eg on routes to Cyprus etc.