This is obviously a pricing error. Walkers Salt and Shake Crisps( Formerly Smiths Crisps) 12 pack is only £1.05 at tesco both instore and on line. This is cheaper than the 6 pack at £1.25.
Normal price for the 12 pack is £2.11
As far as I can see this is not on any special offer and is a mistake.
Available both in store and on line