In message

, at 18:05:11 on Fri, 15 Nov 2013, Recliner
remarked:
I've not seen figures but it looks like the Picc carries many more pax to
and from Heathrow than HEx.

HEx is only intended as a replacement for taxis (ie for people who had
it not existed would have taken a taxi), it's not in competition with
any other rail-based modes.
--
Roland Perry