In message , at 16:56:35 on Tue,
7 Mar 2017, Mike Bristow remarked:

However "Using track that's not often used" isn't really the definition
of a parlimentery train, IMO. A parlimentry train is one that is
run to avoid the hassle of formal clousure procedures. That service
is a peak hours congestion buster.

It could of course be a parly that unusually runs when people need it,
rather than at the most inconvenient possible time.

You're wrong.

Wrong to speculate. Now that's a first.

I've done some digging. The service was introduced
in 2005 or so (albeit in a different form), to use the spare set
to try and reduce overcrowding. The user group has a history of
the "PIXC busters" on their site if you're curious.

If we accept that a parly train is one run to avoid clousure
proceedings, then that train ain't one.

If you want to define it as an occasional train run on on track
rarely used in passenger service, feel free (but I'll disagree with
your definition).

I wasn't. So there's nothing to disagree with.
--
Roland Perry