Shops throw away an estimated 1.6m tonnes of food every year. But more and more are thinking inventively about waste and distributing leftovers to those in need.
A shopping basket filled to the brim with sandwiches clatters along the uneven pavements of the alleyways and back streets of London's Covent Garden. Mark's trained eyes scan the doorways and cavities of the surrounding office blocks and theatres.
He stops and points through the darkness to a figure curled up in a thin blue sleeping bag. Out of the basket he takes a couple of sandwiches. Careful not to wake the sleeping man, he gently places them by his feet. Returning to his basket, he continues into the night. This is the front line - grassroots social work.
Mark's basket is a welcome sight. He walks the streets handing out cups of tea, offering food and chatting with those preparing to bed down for another night in the open. People appear seemingly out of nowhere, grateful to receive what may be their only meal that day.
Chris Stanion has been homeless for eight years. In and out of hostels, he is now sleeping rough. He is offered a sandwich - Wiltshire cured ham on malted bread.
"That shops give away food at the end of the day is good because if it wasn't for these sandwiches lots would go hungry," he says, also clutching a warm cup of tea.
The food is donated by Pret A Manger, a food company selling high-end sandwiches and salads. What the homeless eat was on its shelves hours earlier. Like everyone else, Mark's regulars have their preferences.
"The homemade sandwiches are actually the best," says David, who has been homeless for "a while". "The Pret sandwiches are past their best by the time we get them. The fillings make the bread go soggy and they are kept too cold."
But the beautifully-packaged sandwiches do have some advantages over homemade ones.
"If we left the sandwiches we make next to the rough sleepers they would be destroyed by the elements before they could be eaten - and they would attract the rats," says Mark.
He is a volunteer with the Simon Community, a registered charity providing aid to homeless people throughout central London.
Every week, he and his co-workers pound the pavements of central London and twice a week the Simon Community distributes sandwiches to more than 100 rough sleepers during their soup run.
"A familiar face is important," says Dave Clark, a trustee of the Simon Community. "The soup runs are a good way of keeping in touch on the streets, the food is a way to build up a relationship with these people."
About 98% of Pret's UK and global branches donate a total of 1.7m products to the homeless in some way.
It's not just about feeding them, says Mr Clark. "It's about showing these people a bit of common decency. That's why we like to give them a choice of sandwich instead of just dumping something on them."
The amount of food the company is able to donate varies. After a busy day some shops might not have any leftovers. And it's not just about feeding rough sleepers. The Olallo Project in London is a residential hostel and training centre for EU immigrants. Residents learn computer skills, English and interview techniques.
Before they started receiving sandwiches, the hostel was unable to provide lunch. Now staff can offer residents breakfast, lunch and dinner.
Nicky Fisher, head of sustainability for Pret, knows such initiatives are "good for the brand" and help to provide a feel-good factor for customers. They are also important in fulfilling the company's promise that its stock is always fresh.
The influential watchdog, the Sustainable Development Commission (SDC), estimated shops were throwing away 1.6m tonnes of food a year, so any waste-saving schemes are welcome. Many other firms are also thinking about how to avoid dumping their leftover food on to the mountains of landfill.
Tesco says it has implemented a very efficient ordering system to reduce waste, but what waste there is can be re-used, recycled, or turned into energy. Leftovers fit to eat are distributed to those in need by a charity called FareShare.
Waitrose also works with FareShare, says a spokesman, and 115 branches generate renewable energy from food waste.
The focus needs to be primarily on prevention of food being wasted in the first place, says the Waste and Resources Action Programme (Wrap), which helps UK businesses reduce their waste.
"There will however be instances where there is surplus food in the chain, at both manufacturers and retailers. It is much better that this food is redistributed rather than it ending up as waste."
The benefits are not just environmental; there are commercial considerations too. To be synonymous with helping the homeless is good for a company and strengthens a company's brand, says Jonathan Gabay, of Brand Forensics. The "low-waste" message will also chime with customers in the present period of national belt-tightening.
"Corporate social responsibility has for the last five years, at least, been a key asset for any major brand. Anything that they can give back to the local community is part of that CSR planning.
"And because we are living in an austere society now, I can see why brands want to say to the customers: 'We are not wasting anything. We're giving these sandwiches to people that need it'.
"Maybe they've been doing it for a long time and in the past just been getting on with it, but now people might be looking at sandwiches left on the shelf and thinking 'where is it going?'"