Please don't vote cold just because you are not a member at Costco, as this offer maybe suggests why you should be a member (if you have one near you of course!)....
Just bought two boxes of these at my local store in Bristol this afternoon. I normally buy them from here and they are usually £12.99 a box, which is good compared with Boots etc, but at £7.29 (no VAT on nappies) they are a steal!
They also had loads of boxes of size 4's and 3's as well priced the same. 5's were the biggest size though.
I looked in the current voucher book and there was nothing related to Pampers in there.
I would attach a copy of the receipt but sorry don't know how to do that.