Sainsbury’s and Morrisons do not currently offer member-only discounts in their convenience stores so the total average cost of the grocery basket was the same regardless of membership. The average was £111.83 at Sainsbury’s and £119.29 at Morrisons.

An investigation has found that Tesco, Morrisons and Sainsbury's all charged more for a basket of shopping in their smaller local convenience stores.

The biggest different was at Morrisons Daily, where shoppers paid 21 per cent more on average. Which? found that Sainsbury's and Tesco had less variation in prices, but Nectar members could still be paying an average of 14 per cent more at Sainsbury's Local.

The biggest different was at Morrisons Daily, where shoppers paid 21 per cent more on average. Which? found that Sainsbury's and Tesco had less variation in prices, but Nectar mem