Some groups of people are being "excluded" from accessing lower prices offered by major retailers' loyalty schemes, according to Which? Vulnerable groups in society such as young carers and homeless people may find themselves excluded from lower prices at some stores, it warned.

Many popular loyalty schemes offer lower prices for members - but the consumer group said some shoppers are unable to sign up due to restrictions that are often beyond their control - such as minimum age requirements, having a UK address, and needing an email address or an app.

The consumer group said its findings indicate that, depending where they shop, a 17-year-old single parent living independently may not get a discount on baby food, while a homeless person could have to pay more for a meal deal. Which? looked at major supermarkets' schemes, as well as those offered by health retailers Boots and Superdrug.

Researchers found that customers have to be 18 or over to join loyalty schemes at Lidl, Sainsbury's, Tesco and Waitrose - but 16 at Co-op and Morrisons. For Co-op and Sainsbury's, consumers under 16 can get a junior membership or be added to a parent or guardian's account to access loyalty scheme prices. Shoppers must be 13 to access Boots and Superdrug's schemes, Which? said.

There are also differences in address requirements and whether or not digital access is needed. Harry Rose, Which? magazine editor, said: "Our research shows there are differences between supermarkets and retailers and their loyalty schemes, which mean some people could miss out on the lower prices offered because of factors such as minimum age requirements and needing an email address.

"All retailers should prioritise making their best deals accessible to all customers by implementing changes to their conditions for signing up."

A Boots spokesperson told Which?: "At Boots we are committed to providing great prices and value for money for all customers through a wide range of deals, discounts and promotions. Anyone aged 13 or above with a UK postal address can also join the Boots Advantage Card scheme. Members can benefit from personalised and exclusive offers in-store, online, through our app and in our mailings."

Co-op told Which? that anyone of any age can become a member. For those under the age of 16, to become a Co-op member permission from a parent or guardian is needed. To become a member if under the age of 16, a temporary membership card can be purchased and registered over the phone. A parent or guardian must be present to give their permission during registration.

Lidl told the consumer group that its app Lidl Plus forms part of its commitment to providing customers with the best value. It said this is on top of being a discounter, meaning its actions are designed to give households access to good food at low prices.

Lidl said it remains mindful of those unable to access a smartphone or tablet and continues to offer in-store promotions through Pick of The Week offers. It said its age restriction in place is in line with legal requirements relating to elements within the app such as certain promotions or partner offers, including those where adult consent is required.

A spokesperson for Nectar, the loyalty scheme at Sainsbury's, said: "We strive to make it as easy and convenient as possible for customers to join Nectar. You can sign-up in several ways, including via our website or mobile app, registering in-store with one of our colleagues, or by contacting our Nectar helpline team over the phone."

The spokesperson added that if a customer contacts the Nectar helpline team they can manually register for a Nectar account without requiring an email address or mobile number. Additional cardholders are required to be over 18, except where they are on the account of their parent or legal guardian.

A Superdrug spokesperson said: "As an accessible retailer, we aim to offer great value to all our customers. Every month we give our loyal health and beauty card members access to hundreds of health and beauty products at a lower price.

"Delivery is only available to addresses within the UK and Republic of Ireland, therefore the health and beauty card membership reflects this and is available to residents of the United Kingdom over the age of 13 or Republic of Ireland (over the age of 16). Customers can sign up and register for a physical H&B card or a digital card either in store, online or via the Superdrug app."

Superdrug said customers can sign up in store or online using their name and either an email address, address or phone number. A Tesco spokesperson said: "Clubcard unlocks the best value at Tesco, with shoppers able to save £360 a year thanks to clubcard prices.

"It is easy and free to sign up and join the 22 million UK households who already have a Tesco clubcard."

A Waitrose spokesperson told Which?: "We work hard to give myWaitrose customers a broad range of benefits, including personalised vouchers, exclusive promotions, free hot drinks, magazines and more. Our digital approach allows us to personalise offers and share benefits quickly, easily and securely. Our age and address requirements are in line with some other retailers and reflect our store locations.

"For help with myWaitrose, customers can call our free customer service line at 0800 188 884."

A Morrisons spokesperson said: "Driving strong value for customers remains our number one priority. Together with our Aldi and Lidl price match, our savers range, our vast range of low everyday prices and our More Card - we have thousands of products that not only offer outstanding value on brands and essential items our customers love - but also have the quality they've come to expect from us."

Loyalty scheme requirements compiled by Which?, with the minimum age requirement, the address requirement, and whether digital access is needed:

Boots , 13, UK resident, No

Co-op, 16 (or junior membership for any age if under 16 and using a card purchased by parents), None, No

Lidl, 18, None, Yes - customers must download the app, and need a phone number and email address.

Morrisons, 16, UK resident, No

Sainsbury's (Nectar), 18 (except where they are an additional collector on the Nectar account of a parent or guardian), UK address, No - physical cards are available. If a customer contacts the Nectar helpline they can be registered without an email address.

Waitrose, 18, Resident of England, Scotland, Wales or the Channel Islands, Yes - customers need to have access to the internet and an email address to sign up