If anyone has a CostCo near them they're pretty good - although it costs about £25 a year for membership. After VAT, it's approx £9 for a 49 box of whiskas in jelly pouches, and 'Thomas' lightweight gravel style cat litter is just under £3 for 16L
That's the one in Haydock, St Helens anyway, I assume it would be the same in other store. They alos sell their own brand dog biscuits which are reasonably priced, and some other cat bits and pieces. AND big bags of bird seed, if you like that kind of thing!