I think that BA already started phasing them out now. The 757's at BA will probably be gone in 2005, if not earlier. I don't know anything more about that.
I flew on one from London to Brussels in 1999.
BA is replacing the B752 with A319´s and A320´s. Their new strategy is to reduce seats on most of the routes and if they have big demand, increase frequencies. They are doing the same with the long houl fleet. B777´s (fewer seats) are replacing B744´s.