Lawrence Myers wrote:
I believe BAA insist that all transport within the airport is free. I think
buses between Heathrow Central and the North area are also free.

Yup. Last time I flew from Heathrow I got an ordinary bus from my hotel
just outside the perimeter to the terminal - free. That was in 2003, but
it wasn't the case in 2000, which was the previous time I did the same.