I was close to paying £7 a few days ago for my 2 kids to play in Wacky Warehouse, until the assistant pointed out that if I paid £3 more I could get an additional 4 visits. It's called the Kidz Summer club.
It's a great place to give you a few hours of peace from the kids (sort of). I've been to a few places in Yorkshire over the last few weeks and they all seem to offering the deal. I can only assume this deal is Nationwide.
Alongside the 6 visits to Wacky Warehouse, you also get a booklet of vouchers covering deals to other places such as Chester Zoo, Sealife Centre, Legoland, Camelot, Diggerland, Cadbury World and more. There's also some online merchant deals included so all in all it's a very good deal. All the voucher deals are listed on the following link: http://www.wackywarehouse.co.uk/summerpassport.htm