A recent investigation by consumer watchdog Which? reveals that Tesco and Sainsbury's customers who are not using the Nectar or Clubcard loyalty schemes often pay higher prices for popular branded groceries than shoppers at Waitrose and Ocado. The analysis examined average prices in February, comparing 245 branded items, including well-known names like Heinz, Nescafé, Dove, Kellogg's, and Mr Kipling, by tracking their prices daily throughout the month to determine the average cost per item. These averages were then totalled to calculate each supermarket's overall price for branded goods.

The list features the most popular brands across various grocery categories, based on industry data, and is intended to create a robust sample rather than mirror a typical shopping basket. According to the findings, in February, the average cost of branded goods was highest for Sainsbury's and Tesco customers who did not use the supermarkets' loyalty schemes. While most Sainsbury's and Tesco shoppers use their Clubcard or Nectar schemes, those who haven't signed up, or aren't eligible, have no option but to pay the full price for branded products.

The supermarket with the most expensive branded items was Sainsbury's for non-Nectar shoppers (£942.66), which works out at 14% more than the cheapest retailer in this analysis, Asda (£823.58).

Tesco followed closely, with its non-Clubcard price totalling 11% more (£916.56).

Aldi and Lidl are often named the cheapest supermarkets overall by Which? but they were not included in this analysis as they do not stock a large range of branded items.

According to the analysis, Sainsbury's and Tesco were more expensive for non-members than Waitrose (£899.05), which is known for being more upmarket and expensive.

Waitrose was 9% more expensive than Asda and is a more competitive option for non-loyalty scheme members.

In Waitrose, several products were cheaper, including Amoy Straight To Wok Noodles, which were on average £1.25 at both Waitrose and Morrisons, but most expensive at Sainsbury's and Tesco without a loyalty card at an average of £2.15 - a 72% difference.

Ryvita Thins (Sea Salt & Vinegar) were also cheapest on average at Waitrose at £1.25, but shoppers buying this product at Morrisons, Tesco, and Sainsbury's without a loyalty card would have paid an average of £2.30, making them 84% more expensive.

Which? found that Asda was the cheapest destination for the list of branded goods at £823.58 on average. Some of the biggest price differences include Oral-B Pro Expert Toothpaste, which was cheapest at Asda in February at an average £2.24, while the same product was most expensive at Sainsbury's and Tesco without a loyalty card at £3.95 - 76% more.

The same was true with Sharwoods Medium Egg Noodles, which were £1.28 at Asda but £2.10 at Tesco without a Clubcard - 64% more, on average.

Which? also found that Filippo Berio Olive Oil (750ml) was £4.98 on average at Asda, compared to £8 at Sainsbury's without a Nectar card, 61% more expensive.

However, for customers with a Clubcard, Which? found that the same list of groceries at Tesco cost £837.43 on average which is just 2% more than at Asda.

The consumer watchdog also found various instances of branded products where the Tesco Clubcard price was the cheapest on average. Carex Hand Wash was 95p at Tesco (with Clubcard) but £1.70 at Waitrose, where it was the most expensive - an eye-watering 79% more.

Another example showed Kellogg's Crunchy Nut cornflakes (300g) were £1.55 on average in February, while the highest average price among the supermarkets was at Waitrose (£2.50) - 61% more.

The analysis highlights the dramatic price differences created by supermarket loyalty schemes.

At Tesco, a 200ml bottle of L'Oreal Paris Elvive Bond Repair Shampoo was double the average price for shoppers without a Clubcard, at a whopping £13, compared to £6.50. The higher price was also found at both Morrisons and Sainsbury's.

Analysing coffee prices highlighted even larger price discrepancies. Shoppers at Tesco and Sainsbury's without a loyalty card were charged £8.35 for a 200g jar of Kenco Smooth, the highest price on the market. In contrast, the same jar was £7.00 at Waitrose and £6.32 at Asda, on average. Similarly, for Nescafé Gold Blend, Waitrose had the lowest average price (£6.25), while non-members at Sainsbury's were charged £8.35.

Meanwhile, Which? found that customers who used a Nectar card at Sainsbury's could expect to pay only 3% more than at Asda (£848.56).

Morrisons was 4% more expensive than Asda when using a More card (£858.67), and 5% more expensive without one (£860.79).

Ocado (£867.17) was also 5% more expensive than Asda.

Across the supermarkets, Which? identified other products with drastically different price points. The largest difference in average price was for Tilda boil-in-the-bag basmati rice (4-pack), which was £1 at Tesco without a loyalty card but £2.25 at Waitrose (125%).

Reena Sewraz, Which? Retail Editor, said: "Our analysis reveals a shocking truth and shows the impact loyalty schemes have had on grocery pricing. Branded favourites can actually be cheaper at Waitrose than at the UK's biggest supermarkets for shoppers who don't use a loyalty card - something that would have seemed unthinkable until a few years ago.

"If you've got your heart set on specific brands, your best bet is to shop around, keep a close eye on the unit price, and stock up whenever you see a good deal - otherwise, you're likely to end up paying way over the odds.

"While loyalty cards definitely offer some savings, if you don't use one, you're better off heading to Asda, where the pricing is usually cheaper on a range of branded goods."

A Morrisons spokesperson said: "Morrisons remains committed to providing good, honest value and we're working hard to keep our prices down and competitive so our customers can spend less while still enjoying the quality Morrisons is famous for. In addition, our More Card members can earn Five More Points on every product in store, online and in Morrisons Daily stores and also benefit from personalised offers and money-off coupons on the things they buy the most of. Customers to our Cafés can also take advantage of a range of offers such as our Kids Eat Free promotion, which runs every day, or free refills on all hot drinks."

A Sainsbury's spokesperson said: "We have invested over £1 billion in recent years to help keep prices low and we know more customers are choosing to do their shop at Sainsbury's. We are committed to helping customers access great quality at lower prices and remain focused on offering outstanding value across thousands of products through our Aldi Price Match scheme, Nectar Prices, Your Nectar Prices and our ownbrand value lines."