tim wrote:

"Colin McKenzie" wrote in message
(Heathrow to Gatwick)
and a couple of spurs, to provide something
reasonably direct and about 25 miles long. Main drawback of this route
is it wouldn't interchange with the SWT main line, as it'd use the
Hampton Court and Claygate branches.

As others have said there is no demand for such a link (and if there
were it could be routed over current tracks with little new build).

Demand is generated when Heathrow is so full that regional flights are
squeezed out in favour of intercontinental ones. People then need to
interchange between LHR and another airport to make flight connections -
which is why the link has to be fast.

Colin McKenzie