In message

, at 16:24:21 on Fri, 15 Nov 2013, Recliner
remarked:

Of course, they will have to stop giving "free" rides from T123 to T4 (etc)

The latter won't work, as it's a fundamental requirement for Heathrow in
the modern age to be able to move passengers from one terminal to another free of charge.

But not necessarily by underground train -- lots of airports use
inter-terminal buses, as does Heathrow for air-side movements.

Indeed, but Heathrow's layout means that using buses is extremely
inefficient and slow. It would be a major new fleet and an expensive
operation to run. Far simpler just to let the passengers use the trains,
given that the trains are already there.
--
Roland Perry