I had a warning from tesco a few months ago that on 2 occasions i parked there at night...after the shop had closed for more then 2 hours and was warned if i do this again i will recieve a ticket! its patetic the shop is shut so therefore i am not stopping customers from parking!
Good shout - take pictures of the surrounding area - if there's no signs, if it wasn't a private driveway and it wasn't single/double yellow lines you'll probably be able to get off with it.