Supermarket loyalty card discounts are not always a genuine saving for consumers, a new Which? investigation has cautioned.

The consumer watchdog conducted a study into almost 12,000 products from grocery retailers’ loyalty programme, such as Sainsbury’s Nectar and Tesco Clubcard.

It took a snapshot sample of the loyalty offers available in one day in May 2024, before checking how many times the products’ non-member prices had been active during the prior six months, to work out the ‘usual’ selling price.

It found that for Tesco, 10% of the products it examined had been their non-member price for less than half the time, 5% at Sainsbury’s and 3% at Co-op.

Which? added that consumers should not feel a “sense of urgency” towards buying a item when its discounted, as its research found that for Tesco, 33% of products involved in the study were on offer for more than half the time during the span of 6 months. For Sainsbury’s, this figure was 13%.

The investigation also found that non-loyalty members could benefit from changing to a rival supermarket. It used an example of a pack of Birds Eye chicken nuggets, which was £5.25 at Waitrose – which is regularly named the most expensive supermarket – £4 at Asda, but £5.50 for non-members at Sainsbury’s.

The watchdog concluded in its research that there were still savings to be made at retailer loyalty programmes, with on average Morrison’s scheme saving 25%, Sainsbury’s 24%, Tesco 23% and Co-op 10%.

Which? said: “So if you are able and eligible to sign up to a loyalty scheme, don’t mind handing over your data and want the discounts, you should probably do so – you will undoubtedly pay less at the checkout.”

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Yet it added: “But don’t be tempted to buy things you wouldn’t otherwise have bought, just because the saving looks impressive. In a worrying number of cases, the non-member price may not tell you the full story.”

Which? retail editor Ele Clark said: “We looked at the pricing history of thousands of products and found that, while the majority of discounts were not misleading, there were some questionable non-member prices and some examples that looked like an outright rip-off. Meanwhile some products were always, or almost always, on loyalty promotion, making it difficult to spot a genuine deal.

“Guidance on pricing laws needs to be updated to include loyalty pricing, to help  regulators crack down if businesses break the rules. The CMA should continue to monitor loyalty pricing practices across key consumer sectors and be ready to use its new powers to take action against retailers that don’t comply.”

In response, a Tesco spokesperson said: “All our Clubcard Prices promotions follow strict rules, including considering how they compare against prices in the market, to ensure they represent genuine value and savings. These rules have been endorsed by our Trading Standards Primary Authority.”

A spokesperson for Sainsbury’s said that factors like inflation, out-of-season products or promotions can affect its prices. They added: “That doesn’t stop us following pricing guidance for the industry and offering great value on the products our customers buy most – whether that’s with our Low Everyday Prices, Aldi Price Match or Nectar Prices.”

Morrisons said they are “working hard” to keep prices low and competition for customers, and pointed out More Card members can benefit from personalised offers, as well as shop-floor discounts.

It is not the first investigation the consumer watchdog has conducted into supermarket loyalty prices in recent months. In April it found vulnerable shoppers were excluded from signing up to the scheme, while in May it also warned supermarket spending “challenges” could lead to shoppers overspending.

The research follows a Competition Markets Authority (CMA) investigation that launched in January into loyalty card price cuts, following concerns they could hamper competition and increase prices for those not signed up to the schemes.

In July the regulatory body found “little evidence” that to justify the claim loyalty promotions were unfair to shoppers, however it revealed it was conducting a second investigation into ‘was/now’ promotions to compare supermarket loyalty prices to those charged by rival grocers.