The £800-a-year penalty for doing the weekly food shop at convenience stores

Shoppers who buy from local convenience stores instead of bigger supermarkets could be wasting as much as £800 a year, new figures have revealed.

A regular grocery shop of 75 items, including a Hovis bread loaf and own-brand milk, would cost around £153 per week at a large Tesco or online. However, the same basket would cost £169 in a smaller Tesco Express, according to Which?, the consumer rights group.

Over the course of a year, that racks up to a difference of £818.

Meanwhile at Sainsbury's, a basket of 69 items, including Heinz tomato soup and McVities biscuits, would cost £133 in a large store. In a Sainsbury’s Local, it would cost £145 – adding more than £470 extra to grocery bills each year.

Sue Davies, of Which?, said: “Shopping at a supermarket convenience shop rather than a bigger store comes at a cost – at a time when soaring grocery prices are putting huge pressure on household budgets.”

Food price inflation hit a record high of 13.8pc in January, according to the British Retail Consortium. The cost of fresh food climbed even faster, hitting 15.7pc.

Ms Davies added: “We know the big supermarkets have the ability to take action and make a real difference to people struggling through the worst cost of living crisis in decades.

“That's why we’re calling on them to ensure everyone has easy access to basic, affordable food lines at a store near them, can easily compare the price of products to get the best value and that promotions are targeted at supporting people most in need.”

While supermarket prices often fluctuate, there were “steep mark ups” at both Sainsbury’s Local and Tesco Express stores.

Own-label sweet potatoes were 95p at large Tesco stores and online, but were 37pc more expensive at Tesco Express. Mr Kipling Bakewell slices were £1.27 in the larger stores, but were 28pc higher at £1.62 in Tesco Express.

Meanwhile in Sainsbury’s, a Heinz cream of tomato soup cost £1.15 online and at the bigger supermarket, but £1.37 in a Sainsburys’ Local. Which? also found that Birds Eye potato waffles cost £1.71 online and in the bigger store, but £2.01 at the local.

However, it noted that not all items were more expensive in the smaller shops. Anchor butter, Colgate toothpaste and Magnum ice creams were all 3pc cheaper on average in a local Sainsbury’s.

A spokesman for Sainsbury’s said: “There may be price differences between convenience stores and supermarkets. This is because our Sainsbury's Local stores are located in city or town centre locations and their operating costs, for example rent and rates, are higher.”

A spokesman for Tesco said: “We work hard to ensure our customers get great value at Tesco, whether they shop with us online, in a large store, or in an Express store. Our Express stores offer a range of extremely competitive own brand products, as well as offering great value deals through clubcard prices. Clubcard prices offer customers up to 50pc off on thousands of lines – from frozen food to branded cupboard fillers – helping them spend less with us.”