How much would you pay for food in a cafe which does not have any prices on the menu? And how would you decide what the price should be, if you knew the food you were going to be served was originally destined for the bin? That’s the dilemma facing customers of a new wave of cafes opening around the country.

There are at least 10 “waste not, want not” cafes, from Skipchen in Bristol and the Real Junk Food Project in Leeds to Save the Date in London; they operate on the principle of using “intercepted food” – food that would otherwise be thrown away by supermarkets and wholesalers – on their menus, while letting customers pay what they feel their meal is worth.

At the Saltaire Canteen, a pay-what-you-can cafe in Bradford, Duncan Milwain’s aim is not just to reduce food waste but also to act as a community hub, redistributing food to people in the area who need it most.

Customers order … and at the end of the meal are invited to put a donation in an envelope. There's no obligation to pay

“Anyone can come in here and have a meal. It’s entirely up to them if they want to pay for it,” he says. Everything except the drinks is served on this basis. “The reason we charge for drinks is because there are two cafes opposite and we thought it would be unfair competition,” he says.

He explains how the cafe, which is mainly staffed by volunteers, works: “People come in, pay for their drinks, then get seated. There’s a chalk board with the menu for that day. Customers order what they want, the food is delivered and at the end of the meal they are invited to put a donation into a brown envelope. We always emphasise that there is no obligation to pay.”

The manager and only paid employee, Stacey Farrar, says that so far everyone has made a contribution. “The donations have been absolutely amazing. We had somebody in for a soup and piece of cake the other day, who put £15 in an envelope. Yesterday, a gentleman gave us a pound for a pasta dish and donated £100. The lowest amount we’ve had was something like 28p. But they know they’re not getting steak or lobster, and they understand the concept.”

Jim and Lisa Barton with their daughter, Ida. Photograph: Lorne Campbell/Guzelian

Jim Barton, a youth worker from Bradford, and his pregnant wife, Lisa, who is a probation officer, travelled from their home in Apperley Bridge with their three-year-old daughter, Ida, to support the cafe.

A regular at Armley’s Real Junk Food Project, Jim is a fan of independent businesses and charities that are ethically sound. “I think as a society we waste far too much,” he says. “People have been reclaiming food from supermarkets for a long time – this is just the next step.”

He and Lisa ordered a soup and a potato bake. They paid £5 plus a £1 tip for it in the end. “I just thought that was an honest price to pay. If I was to order a similar sort of meal from another cafe I’d guess that would probably be the price that they’d charge. I also thought that the food is being up-cycled – it’s not top end. So I weighed that up in my mind as well.”

Paul and Lynne Smithson from Pudsey had never heard of the “pay what you think it’s worth” concept before. “This cafe has a lot of win-wins. There’s a benefit to us, there’s a benefit to charity and the food is not going to landfill,” Paul says.

Lynne ordered a mince pie and a coffee. “I put £2 in the envelope [for the mince pie]. It’s probably worth about £1 but I wanted to give a bit more because it’s going to charity,” she said. “I think people will pay what they can afford.”

The day’s menu is written on a blackboard at the Saltaire Canteen.

Later, the couple also ordered two celery soups, for which Lynne thought she would pay £10. “Oh wow, that’s a lot for two soups,” Paul says. But they agreed that they would feel awkward if they felt they had ripped off the cafe.

The menu at Saltaire Canteen is understandably limited. On the day my family and I visited it was celery soup with croutons; bacon, potato and onion bake with festive greens; creamy potato soup and focaccia; apple cake; baked ginger cake; and apple crumble. The food was all made on site from intercepted produce.

Milwain shows me the small kitchen. “There’s a sense that it’s a community kitchen – that doesn’t mean the food will be poor quality,” he says. “I’m a bit of a fan of Yotam Ottolenghi. I want to produce flavourful food.”

I had the celery soup and my husband chose the only gluten-free option: apple cake. I paid £5 for my choice and Josh £2.50. We agreed we’d paid over the odds for food we wouldn’t race back to eat. But we felt the cafe’s ambience, its location and the knowledge that the money was going to a good cause made it worth what we paid.

Reflecting on whether the location influenced our decision to pay more, Jim Barton says: “It’s quite middle class around here, and therefore it will attract middle-class people [who will perhaps pay more]. The original cafe was set up in Armley – which is a very poor, deprived part of Leeds. It’s used very much as a hub for everybody – the unemployed, asylum seekers and refugees.

“People in the neighbourhood know that you can go there and get a good, healthy meal at a fair price that they’re able to pay.”

Pay-what-you-want pathfinders

• Some UK theatre companies and arts festivals have introduced a “pay what you think it’s worth” model. Slung Low, a Leeds theatre company, has been presenting its shows for two years on this basis. Artistic director Alan Lane says they adopted the policy as part of a transparency drive. The average donation is £7.50, which he believes for an hour’s production is about the right amount. They have a £1 bar and serve free tea and coffee. Other theatres such as tThe Arc in Stockton-on-Tees and the Park Theatre in Finsbury Park have also introduced this policy for some performances. The Greenwich+Docklands International Festival puts on free summer events each year. But, a spokesperson says, people are encouraged to put money into a collection box or text a voluntary contribution.

Stephen King released his novel The Plant through the internet.

• Stephen King, dabbled in honour-payment for a novel he released digitally in 2000. Chapters of The Plant were delivered in instalments on his website. Readers were asked to pay $1 for each chapter downloaded, either before or after reading. He pledged to keep writing if at least 75% of his readers complied. At the time he reportedly said: “If you pay, the story rolls. If you don’t, the story folds.” it. Early sales were buoyant with 120,000 downloads of chapter one. By the fifth chapter this had dipped to 40,000. King received a total of $721,448 (£485,000) from readers. After expenses, he reportedly made a profit of nearly half-a-million dollars. He ceased writing after six chapters – they are now free to download on his website.

• In 2007, rock band Radiohead released their album In Rainbows digitally on a pay-what-you-think-it’s-worth basis. At the online check-out, instead of a price appearing, fans were shown a prompt that said “It’s up to you”. This was the first album of its kind where customers were able to determine what they wanted to pay. A year after its release, Rolling Stone magazine reported that more people had downloaded the album free than had paid for it, but it had still generated $3m in total sales.