Don’t worry about trying to find us, says Adam Smith, founder of a new supermarket-style enterprise whose mission is nothing short of saving the planet: “You’ll see the queue outside.”

Sure enough, a dozen or so people are waiting at the doors of his Sharehouse shop in Sheffield, ahead of opening on the afternoon I turn up. They have come – and will continue to crowd in for the next two hours – for two main reasons.

The first is because the choice of groceries inside this unrefurbished warehouse is phenomenal: crates of fruit and veg, baskets of breads, a deli counter offering pies and pates and pickles, tinned goods and cakes. Lots of cakes. Very occasionally, you can get blast chilled chicken from Nando’s here – “although,” says Smith, “it flies out the door pretty quick”.

The second reason all these customers keep turning up is because of the price for everything in here: “Pay whatever you feel.”

People come in, fill their baskets and then hand over as much or as little money as they want. Some people do weekly shops for a fiver, and that’s fine.

What’s the catch? There is one, of course. Everything here has been salvaged from supermarket bins, restaurant leftovers and wholesale market waste. Edibles otherwise marked for landfill have been saved and piled high. Smith once got called by a food bank with a surplus of donated tins and nowhere to store them. He collected them in his van, stuck them in store and watched them get snapped up.

Local branches of Morrisons, Sainsbury’s and M&S all have his team take their unwanted goods. Today there is an abundance of potatoes here. “Too wonky even for the wonky range,” Smith explains with a shrug.

This, then, is the Real Junk Food Project, an enterprise created by the 32-year-old one-time executive chef with the aim of reducing the UK’s vast quantities of food waste, while helping people struggling – or simply seeking a bargain – in austerity Britain. And it’s proving more popular than he ever imagined.

After he set up his first Sharehouse shop in Leeds in autumn 2016, the scheme has expanded at a rate the Big Four would be proud of. Six more stores have opened in the interim – this one in Sheffield, along with Birmingham, Brighton, Durham, Wigan and Chester – with three more, in Halifax, Wakefield and Keighley scheduled for late summer. Each one saves an estimated six tonnes of food from going to landfill every week. Along with a series of Real Junk Food cafes and Real Junk Food school projects (more of which shortly), Smith estimates that food goes to 25,000 people across the UK every week.

The Real Junk Food Project’s Sheffield Sharehouse store (Real Junk Food Project)

And it’s all sorts of people too: families, old folks, millennials and the just about managing. Last month, this particular outlet had a massive batch of asparagus come in. “We put it on social media and it went a bit crazy,” says Jo Hercberg, director of the Sheffield project. “We got a whole new foodie customer base from that.

“We make no bones about what we offer,” she continues. “Our stock is what most shops would chuck out. Maybe it’s passed its best before date, maybe the lettuce has a browned at the edges, maybe a tin is dented. But we trust our customers to understand that. They do what human beings have always done: they use their sight and smell, and if something seems okay, they’ll have it.”

The contradiction that inspired the Real Junk Food Project is a bizarre but real one. Every year, according to UN figures, 1.3 billion tonnes of food are thrown away. Yet, simultaneously, some 800 million people across the planet are malnourished.

This paradoxical waste and want first struck Smith while working on an Australian farm five years ago. The surplus there was so pronounced they would feed courgettes to pigs because it was cheaper than buying feed.

“But in Sydney there are hundreds of people on the streets who can’t afford to eat,” he says. “It’s that contradiction I want to solve.”

Cakes and breads at the Sheffield Sharehouse store (The Real Junk Food Project)

He returned to his home town of Leeds and founded the project. It was a cafe at first, a single outlet opening for a couple of lunches a week in a converted corner shop in the city’s Armley district. But it used the same principle that remains at the heart of the enterprise today.

“Myself and volunteers persuaded local supermarkets to let us take what they were throwing out,” he explains. “It was pushing an open door because disposing of that waste costs money, so having someone come and take it was a win-win. Then we cooked it all up at the cafe.”

Menus varied depending on what they were given: curries, lasagnes and hot pots. Diners were told to pay what they wanted – or even asked to volunteer themselves – in return for the meal. “It was just an experiment,” says Smith. “We couldn’t believe how quickly it took off.”

Within three months a second was opened by volunteers in Bristol. Then they kept opening. Today there are more than 120 worldwide, including in Germany, South Korea and Israel.

Each new venue is given basic rules to follow – 90 per cent of food used should be designated waste, for instance – but, largely, they’re left to their own devices as part of a franchise system.

The other thing which happened was Smith started receiving calls from places asking him to take their food waste – which finally led him to the idea of his supermarket-style shops.

Managers Rene Meijer and Jo Hercberg at the Sharehouse store (The Real Junk Food Project)

“We were getting too much food just for the cafes,” he says. “So why not sell it as pay-what-you-feel groceries? The variety of places it comes from, you wouldn’t believe. I got a call the other day from a shipping yard. Someone hadn’t paid rent on a container and they wanted it emptying. It was thousands of tins of peas.”

He points it out in the warehouse, which is attached to the shop. “Want to take a couple of cans?” he asks.

The shoppers here seem to love the place. They come in, browse, basket in hands, taking their time, asking volunteers question about produce and products.

One is Fareesa Awan, who lives near the Sheffield store. “A friend told me about it,” she says. “She told me you go in looking for a bargain but end up walking out with a week’s worth of food. I thought, ‘That I have to try’. It’s wonderful. I don’t do my shopping here because you can’t always guarantee what they will have in but I’ll come and pick up some fruit, veg, cakes for the children – and my husband. I like to cook and there’s always something unusual here which you can pick up for next to nothing and then experiment with.”

I ask if it bothers her that some of it is passed its best before date and she laughs. “I trust myself to decide what’s OK,” she says. “These dates – who decides them? They’re not necessary. Besides, once it’s in our house it does not last long. Big family, lots of visitors. The food soon goes, so it is good to get it cheap.”

Adham, a student who asks not to give his last name, says he pops in occasionally after reading about the place on social media. “Do you know what it is?” he asks, “I read they have KFC chicken sometimes [they do] so I’m hoping to get that – but, mate, so far there’s never been any in. But I still end up walking out with, like, grapes or milkshake or nuts or whatever. I took my mum some olives. She was going: ’Olives? What have you been up to? Why are you getting in my good books?’ I didn’t tell her I’d got them almost free. I should. Maybe she’d come here.”

Back in store, the big question might be: just where does the money come from? Each shop typically has an average of 10 staff (along with dozens of volunteers) and requires large premises, so how does it fund itself?

“With difficulty is the honest answer,” is Hercberg’s rueful reply.

Each enterprise runs its own finances. Some run paid-for catering events. Others have contracts to provide after-school dinner clubs. One or two have been given council or charitable grants. Customers are often generous when paying for their shop.

“But it’s a struggle,” says Hercberg. “There’s not much money giving away food – who’d have thought?”

The Real Junk Food Project’s Leeds Sharehouse store (The Real Junk Food Project)

Legally, there have been issues too. The Real Junk Food Project works in the grey area of food regulation, and in April last year the Leeds store faced prosecution from West Yorkshire Trading Standards. It was found to have 444 items beyond their expiration date – distinct from “best before” dates in that, while the latter is advisory only, it is illegal to supply a food which has passed the former.

“But, as we said, our food has fed more than a million people and not one has ever reported getting ill,” says Smith. “So we know what we’re doing.”

In the end, the project was given a slap on the wrist and told not to stock food beyond its expiration date in future. “I still don’t agree with that,” Smith says. “These dates are arbitrary. They’re there to scare you into buying more often, but this is the law so we comply.”

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As the Sheffield shop starts to wind down today – it opens for two hours Monday to Saturday – I ask Smith how much bigger the Real Junk Food Project can get.

“My dream would be to see a zero-food waste society in the UK,” he says. “But I don’t know if that’s ever going to happen. I’ve spoke to party leaders – I won’t say who – and they’ve told me there’s no votes in this. I’ve been invited down to Westminster but I’ve stopped going. They listen, ask questions, and then do nothing.”

He thinks about it all for a moment and, here, amid mountainous piles of pesto and mayonnaise, seems momentarily overwhelmed.

“But we keep at it,” he says. “I’ve been doing some consultancy work with a supermarket. Their managers in London got alarmed by how much food they were giving us every day. I think they calculated it up and realised how much money they must be losing by throwing so much stuff out. So, they asked us in as a consultancy to help them reduce their waste. That will mean less for us to take away each day but that’s a good thing.”