The Isle of Sheppey on the Thames estuary is ranked among the most deprived areas of Britain and like millions of people living on low incomes, its residents are grappling with the rising cost of food and fuel. All are bracing themselves for even harder times this winter.

In a pub car park on the island early one morning last week, a small group of locals stood clutching shopping bags, awaiting the arrival of the “Sheppey Support Bus”, a mobile community supermarket that offers surplus food and free fruit and vegetables for a £3.50-a-week subscription fee.

“It’s a bit of a lifesaver,” said David Fuller, 66, who lives on a monthly pension of less than £1,000.

“Everything has gone up — food, gas, electric bills — but pay has stayed the same. Three years ago I didn’t need somewhere like this, but now I do.”

It is an increasingly familiar tale as food bank usage shoots up across the UK. But the sponsors’ logos on the side of the double-decker Sheppey Support Bus tell a less well-understood story about how the charitable and voluntary sector is now an integral part of the UK’s social safety net.

After a decade of austerity that saw local government funds cut by a third in real terms and the value of many welfare benefits falling to a “historic low” according to the Joseph Rowntree Foundation, charities are playing an increasing role in helping people to make ends meet.

But the charitable top-up comes only in areas like Sheppey that are fortunate enough to have a volunteer network. Too many others are getting left behind, warn experts in the voluntary sector, and the outlook is bleak with the Bank of England forecasting a protracted recession and the worst squeeze on living standards in 60 years.

The Sheppey Support Bus was the creation of the Oasis Charitable Trust, which runs a local academy school. The trust pulled together a network of backers to provide the service, including charities such as the Salvation Army and Feeding Britain, supermarket chain Wm Morrison from the private sector and local parish and borough councils.

Lynne Clifton, the Salvation Army officer on Sheppey, said the bus also looks to provide wraparound services, including debt counselling, help with literacy, and mental health services.

“Recently a regular came in, and I could tell she didn’t look her usual self,” she said. “When we had a word she burst into tears, and took out a huge gas bill for £2,000. We were able to help with meter reading and dealing with her energy company.”

Everyone involved in the Sheppey Support Bus enthusiastically lauds its work helping families that can no longer cope, often after getting deeper into debt as a result of the Covid-19 pandemic.

But experts warn that relying on the voluntary sector to pick up the pieces risks overstretching it and entrenching deep-seated inequality across the UK.

Maddy Desforges, chief executive of the National Association for Voluntary and Community Action, whose members support about 200,000 local charities and voluntary groups nationwide, said the sector was now increasingly “backfilling” for the state.

“The state is relying on volunteers in a way I don’t think is helpful,” she said. “So of course, during the pandemic volunteers stepped in, but one of my worries is that the state is now turning to volunteers to shore up services.”

The first challenge of relying on charity to fill gaps left by the government is that the same cost of living crisis that is heaping demand on the sector is also crimping its ability to raise funds. Charities are also buffeted by the same economic headwinds as businesses: rising energy bills, tight labour markets and inflation eating away at the real value of donations.

Analysis by Pro Bono Economics, a think-tank that supports charities, showed that even before the current crisis, the sector was becoming increasingly reliant on public fundraising as the value of government contracts fell.

And the cost of living crunch is already affecting donations, which totalled £10.7bn last year. A regular survey by the Charities Aid Foundation found that in the first quarter of 2022, 4.9mn fewer people had donated over the past 12 months, compared with before the pandemic.

But experts warn that the more fundamental issue about increased reliance on charities for social provision is that it risks entrenching inequality because many of the poorest areas nationwide are least well supported by charities.

Parliamentary research looking at England’s 225 most “left behind” neighbourhoods found that people in those areas received, on average, £7.77 in national charitable grant funding per head, well below the national average of £12.23. Half received less than £5.

“We know the charitable sector is much stronger in richer areas,” said Lord Gus O’Donnell, a former cabinet secretary and chair of Pro Bono Economics. “In poorer places the chances of having community help through the charitable sector is much weaker, and the amount of giving is lower, so you’re in a vicious circle, reinforcing inequality.”

Desforges is equally concerned. “You’re relying on those people who are already living difficult lives, so it’s almost the opposite of levelling up,” she said, referring to Boris Johnson’s flagship policy to reduce regional inequalities.

The outgoing prime minister was driven in part by a sharp shift in the number of seats to his Conservative party from Labour in the poorest parts of the UK at the 2019 general election.

Johnson has sought to capitalise on the community spirit which came to the fore during the pandemic. He commissioned a report from the Conservative MP Danny Kruger on how charities might help with levelling up. But as the UK awaits a new prime minister next month, there is broad scepticism in the sector about the government’s commitment to reducing inequalities.

The government said it recognised the regional inequalities, which was why it was “pressing full steam” ahead with its levelling up agenda while offering a £37bn package of emergency support to households to tackle immediate cost of living issues.

“By investing in the areas that need it most, improving schools, supporting regeneration and generating higher paid jobs we will improve the lives of the poorest in areas across the UK,” it added.

However Kruger said the next prime minister urgently needed to tackle the issue more aggressively, perhaps by using some of the almost £1bn of dormant assets in the UK financial system to endow a community wealth fund. “Fixing this is about money and power: money for social infrastructure and power for local places,” he added.

Will Tanner, director of Onward, an influential centre-right think-tank that has helped to shape the levelling up agenda, said empowering local volunteers was crucial because they were often better at delivering services people needed than central or local government.

“While we should worry about the distribution of that support, that isn’t an argument for not encouraging such activity where it is present,” he said. “The question is, ‘Can it be seeded and encouraged in areas where it is currently lacking?’”

Steve Chalke, founder of the Oasis Trust, agreed but said the government should recognise that to promote more collaborations like that on Sheppey it needed to work with charities in a more equal partnership. “We need a new civil contract between government and the voluntary sector; one built on respect and trust rather than servitude,” he added.

Another example of grassroots empowerment can be found in Northwood, the most deprived part of Kirkby, a satellite town of Liverpool. The area is one of the 150 poorest parts of the UK, which were selected to receive £1mn each over 10 years as part of a £200mn National Lottery-funded initiative called Big Local.

In Kirkby the money funded Northwood Together, a community project that has supported everything from a “pop-up” second-hand clothes shop to food drop-ins and cooking classes.

Lisa Cover, community development manager, said the pandemic had hit the poorest families hardest because many relied on the grey economy or part-time jobs that were not covered by government job support schemes.

The group’s food drop-in, which is supported by donations from the local Morrisons and Liverpool football club, is open all day. And — unlike some local government services — it comes with no strings attached.

“We started to get a lot of discreet inquiries, saying ‘Do you have to be on benefits to come?’ and we explain ‘No, just come on down’,” said Cover. “It’s often working people you see now that aren’t coping.”

A group of Northwood Together board members, who are all local people, said the Big Local scheme had been invaluable for families on the edge of destitution who are now dreading the coming winter, with average annual fuel bills predicted to exceed £4,000 early next year.

Ally Middleton, board chair, said government support of up to £1,200 for the poorest families with their energy bills “won’t feel like it touches the sides” for households that were already in debt.

She added that many children were going hungry at holiday times without school dinners. She recalled one boy who attended an event and after eating his hot dog quietly came up and asked if he could take something for his brother who was at home, and hungry too.

As in Sheppey, the team of volunteers in Northwood are full of enthusiasm for what they have achieved, while recognising it is made necessary because of a wage and welfare system that leaves too many people, including some of those in work, falling through the cracks.

“It may only be a sticking plaster but at least we’re stopping people bleeding out,” said Middleton.