Rob,
CostCo: - Its a yankee Cash & Carry down at West Thurrock and on the North Circular at Edmonton. Prices are good
but its not worth the trip just for the batteries.
We regularly buy AA and AAA as the kids seem to eat them or at least their hand held's games machines and MP3 players do.
I'll drop you a PM next time we are heading in that direction...
Cheers
Steve