Thanks mate, but it's too big for A4. I had thought about just using a 2mm plasticard but that would have to be joined too. The annoying thing is I've seen loads of the stuff before but never bought any because I didn't need any at the time (I know, it's not the wargamer's way!) and I thought if I did need any it'd be there.
There's a place near work I can try tomorrow if I can get out.