They were the best thing since sliced bread. Supermarket bakeries, with their aroma of oven-hot goods, attracted customers who wanted a fresher product than the standard pre-packed offering.

But campaigners have cast doubt on just how fresh these baked goods are, with four big supermarkets accused of misleading claims and breaches of consumer protection regulations.

The Real Bread Campaign, run by Sustain, has submitted a trading standards complaint over how Sainsbury’s, Tesco, Lidl and the Co-op are marketing their bakery products.

Of Sainsbury’s, the group said that its bakery section products use claims including “freshly made every day” and “freshly baked bread”.

The supermarket giant is switching from scratch baking, essentially making products from basic ingredients, to rebaking bread made elsewhere, which the campaign group says means the “claims are increasingly unrepresentative of the company’s in-store bakeries in general”.

Last month, Sainsbury’s announced that more of its in-store bakeries would move to a “bake-off model” as part of wider proposals that could see 1,500 roles cut across the business.

The supermarket did not respond to a question from the Guardian about how many of its stores still use baking from scratch.

A spokesperson said the company reviewed its “bakery services and recipes earlier this year” to ensure “good food affordable for everyone”.

The spokesperson said: “More of our stores now bake pre-prepared dough in-store, as it allows us to offer customers the best quality in-store bakery products at great value. Our bakery items are also clearly labelled in line with legislation and trading standards.”

On Monday 10 June, the campaign group submitted a complaint to Oxfordshire county council trading standards.

It has made similar complaints about Tesco, with the group accusing the supermarket of misleading claims including saying “expertly baked in store since 1968”, and “baking fresh from our ovens every day” on packaging, store displays and its website.

The Real Bread Campaign claims Tesco uses such marketing at stores where no bread is freshly baked from scratch on-site, at which baking expertise is not required, and in ones that did not exist in 1968.

Tesco bakeries have products made from scratch in 400 out of almost 3,000 UK stores.

A Tesco spokesperson said: “In some stores where we don’t have the space to bake everything from scratch, we work closely with our bakery suppliers who prepare dough for us that trained colleagues bake every day in store.

“The signage we use in each individual store reflects the different ways we prepare bread, and our approach has been agreed with our trading standards primary authority.”

There are regulations protecting consumers from falsely described or presented foods, and it is primarily down to trading standards to enforce the law.

The campaign also challenged Lidl’s use of claims including “our fresh in-store bakery” and “baked for you throughout the day” despite not baking any bread fresh from scratch at any of its UK stores. Instead, pre-made products are put into ovens to be baked for a second time for a browner, crisper crust, the group said.

Lidl has been approached for comment.

A complaint was also submitted about how the Co-op labelled and marketed its “freshly prepared”, “sourdough” baguette, which the campaign understood was manufactured and baked by a third party and then baked again in Co-op stores.

Four months later, the Real Bread Campaign claims it is still chasing a resolution from Manchester city council, the company’s primary authority for trading standards.

A Co-op spokesperson said: “As a convenience retailer, we pride ourselves on offering an affordable and great quality in-store bakery range for our member owners and customers – including our much-loved Irresistible sourdough baguette which is freshly prepared and baked by trained colleagues across our stores every day.”

Manchester city council said it is looking at the referral and has been in contact with the Co-op and the Real Bread campaign.