Millions of UK shoppers are not able to access lower prices at some of the UK’s biggest supermarkets, new research from Which? suggests.

The consumer watchdog looked at the joining requirements of loyalty or savings schemes across supermarkets including Asda, Co-op, Iceland, Lidl, Morrisons, Sainsbury’s, Tesco and Waitrose, breaking down the minimum age restrictions, address requirement and whether digital access is needed.

Which? found that only Co-op and Morrisons offered 16-year-olds access to sign up to their loyalty schemes, while the other retailers had 18 years-of-age requirements. Sainsbury’s, however, does allow an individual younger than 18 access if they are added to the card of a parent or guardian.

When looking at address requirements, Asda, Co-op, and Lidl had none, however, to use Iceland’s savings bonus card or Morrisons scheme you must be a UK resident, for Tesco and Sainsbury’s you need to have a UK address, and at Waitrose, you must be a resident of England, Scotland, Wales or the Channel Islands.

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While digital access was not required to sign up at Co-op, Morrisons, Sainsbury’s or Tesco, it was mandatory at Asda and Iceland, even if using a physical card.

At discounter Lidl, digital access is needed, including having to download the app, with an email address and phone number required, while Waitrose also asks for an email address and internet access to sign up.

The consumer watchdog, which is concerned that certain groups of people are excluded from accessing lower prices because of their age, lack of address or level of digital access, is calling on retailers to find a solution.

Lidl told Which? that it offers non-member promotions and that its age restriction is industry standard and in line with legal requirements relating to its app, including where adult consent is needed, while Sainsbury’s said that it does want to make it easy for customers to join its Nectar loyalty scheme.

Tesco said that its customers had not raised concerns over age eligibility criteria and Waitrose said its age and address requirements were in line with some other retailers and reflect store locations.

Iceland has been contacted for comment.