I've got a UGC pass that I use in Crawley and, while it is good, they don't let you book over the internet; you have to call a number for 3 mins at 25p a minute. I've never done this but as I understand it you can't book more than one ticket at a time or non-unlimited card seats at the same time either. So if you are going to a showing that has allocated seating you won't all be seated together as bookings have to be made separately.
Not that I would want to go to a showing with allocated seating in Crawley anyway, as you might have to sit in a chair from which one of the local kiRAB has removed the armrest paRAB!