Staple foods like rice, spaghetti, baked beans and tea bags can cost more than three times as much if budget versions are unavailable, according to a study.

Watchdog Which? has called on supermarkets to ensure they stock value ranges across all outlets after discovering how much more consumers are paying when cheaper versions are not available – which it said was often the experience of those who have to rely on local convenience stores.

In the worst example, Which? found shoppers could be faced with having to pay 246% more for Asda’s standard own-brand Easy Cook Long Grain White Rice (1kg) at £1.80 than the 1kg Just Essentials 52p option.

If no own-brand options were available, Ben’s Original Long Grain Rice (1kg) was £4.85 – 833% more than the budget range version.

At a Tesco store, where the budget 52p Grower’s Harvest Long Grain Rice (1kg) was unavailable, shoppers had to pay £1.25 for the supermarket’s own-brand Easy Cook Long Grain Rice (1kg) – or 140% more.

Which? found Ben’s Original Long Grain Rice (1kg) at £5.25 at Tesco was 910% more than the budget range version.

Which? found the same price differences at Sainsbury’s as at Tesco, and also found that Hubbard’s Foodstore Spaghetti (1kg) at Sainsbury’s was 56p while the standard own-brand alternative Sainsbury’s Quick Cook Spaghetti (500g) was 75p, an increase of 168% when comparing the price per 100g.

Meanwhile, branded Napolina Spaghetti (1kg) was £2.50 – 346% more than the budget version.

At Morrisons, budget Savers Baked Beans (410g) were 27p but standard own-brand Morrisons Baked Beans (410g) were 48p – 78% more.

Heinz Baked Beans (415g) were £1.39, a gram for gram increase of 396%.

At Tesco, Which? found budget Stockwell & Co 80 Tea Bags (200g) were 78p, while the standard own-brand Tesco 80 Teabags (250g) were £1.10 – 41% more.

Which? acknowledged there were likely to be differences in quality and ingredients between the different ranges of products.

But it said shoppers who rely on supermarket convenience stores were likely to have a more limited choice than those who shop online or in larger stores.

Previous Which? research found essential budget line were hardly ever sold in supermarket convenience stores.

Which?’s inflation tracker shows that the overall annual rate of grocery inflation slowed to 12.5% in August, the lowest figure recorded since September 2022 and a considerable fall from the high of 17.2% earlier this year.

Morrisons has started to stock 10 budget range items in 500 of its Daily stores and said 30 more will follow.

Tesco has also vowed to swap branded goods with cheaper branded or own-brand alternatives in Express stores.

Sue Davies, Which?’s head of food policy, said: “As millions struggle with increased food prices and other high household bills, it’s staggering that shoppers face paying over three times more for items if they can’t get to a larger supermarket.

“Which? is calling on all major supermarkets to ensure expensive convenience stores are stocked with a range of essential budget ranges so that hard-pressed customers can afford important staple foods to feed themselves and their loved ones healthily.”

A Sainsbury’s spokeswoman said: “We are acutely aware of the pressures facing millions of households right now and our number one priority continues to be doing all we can to keep prices low for our customers.

“We offer our customers choice and value, whether they shop in our supermarkets or Sainsbury’s Locals. 100% of our convenience stores stock more than 200 core own-brand items and 431 of our convenience stores also stock our best own value ranges like Stamford Street.

“The range of products in our convenience stores is carefully chosen to meet local customer demand.”

Andrew Opie, director of food and sustainability at the British Retail Consortium, said: “Food retailers are doing everything they can to offer the best value for their customers despite high costs throughout the food supply chain. There is clear progress by retailers in the efforts to support consumers, with Which’s own data showing grocery inflation at its lowest level in 11 months.

“The Competition and Markets Authority, the UK competition regulator, recently published its report showing how operational profits at supermarkets fell by almost half to just 1.8%, as retailers protected their customers from rising costs. Furthermore, we have seen retailers cutting prices of hundreds of products in recent months – something barely acknowledged by Which.

“When noting the price difference between budget and premium products, Which? should be celebrating the hard work by retailers to bring down the prices of their value lines, and delivering the best value for those most affected by the cost-of-living crisis.

“Rather than vilifying retailers, Which? should support their readers by providing clear information about the many products that are falling in price, and the best alternative options for those products which have seen price rises.”