In message , at 13:34:53 on Tue, 7 Jun
2011, tim.... remarked:
Westbury is a poor example. It's a tiny place that just happens to have a
main line next to it. There are bigger places in the area that get no
trains at all!

And which therefore use Westbury as a railhead. (I used to drive there
from Frome, for example).

And can equally use Bath as a railhead

In the general case - you have to be kidding! Dreadful journey, twice as
far, horrible parking. For the Olympics, maybe people willing to drive
for half an hour at 1.30am could use Bath instead.

Places West of Westbury are served by later trains running via Bristol

The 20.35 is listed as the last train to Plymouth, the last to Taunton and
Exeter is 21.45 (I'm ignoring the sleeper).

Why? What wrong with the sleeper?

Because there are a very limited number of sleeper routes (and sleeper
capacity), and so you can't rely on a sleeper train to mop up all the
late stragglers from the Olympics. You need other trains too.
--
Roland Perry