The watchdog said: "Waitrose was the most expensive for our bigger shop every month except September, when Sainsbury's was priciest (for shoppers not using a Nectar card)", reports Birmingham Live.

Sainsbury's Nectar provided a £4 discount on the smaller shop and more than £30 on the bigger shop too, while Morrison's More card savings were much less (£2.31 and £12.80). Want the latest ...

Sainsbury's shoppers have been issued a £624 warning over holding a Nectar card. Those who are subscribed to the supermarket giant's loyalty card scheme have been warned over the difference in ...