I've just bought a leisure battery for my camper and one for my portable power pack from a company I encountered at the Stafford Classic Bike Show in April. Their knowledge, range and pricing impressed me (but, as some of you know, I have a low threshhold of satisfaction so don't set too much store by that!) so it might be worth giving BOM Batteries a call on 01427 753652.
They're in Haxey, near Doncaster.
Regards
Nick D.