John takes a brief break from sweeping the polished floors in Swansea’s celebrated indoor market to ponder his momentous decision to vote Leave in the EU referendum.

“If I had the chance, I’d change my vote,” he says. “There has been talk of a lot of job losses and I’m not happy with that. It’s just a mess. I don’t think they know what they are doing.”

He is not the only Welsh voter switching sides amid dire warnings of economic turmoil, food shortages and threats to jobs if Britain leaves the European Union without a deal next March. A new constituency-by-constituency model by data scientists at Focaldata, which uses new YouGov polling, has found that 14 Welsh constituencies swung from Leave to Remain this year, putting Wales firmly in the pro-EU camp.

One of the biggest shifts was in Swansea, a solidly Labour city which saw a near-13% swing to Remain in its deprived east. This would give EU supporters 51% in the Swansea East constituency, which voted 62% for Brexit in 2016, and deliver a Remain vote of 56% across both the city’s constituencies.

In a cafe near the market, Geraint Davies, the passionately pro-EU Labour MP for Swansea West, puts the dramatic swing down to voters’ frustrations with the tortuous negotiations, and a growing realisation that the tempting promises about inward investment and jobs will come to little in the end.

“People voted to leave the EU on the promise of more money for the NHS from the membership fee, access to markets and more trading opportunities, and taking back control of our borders,” he says. “People are now realising that a lot of those promises won’t be delivered.”

Davies also points to a growing feeling that Swansea is losing out rather than benefiting from Brexit. Recent plans for a £1.3bn tidal lagoon in Swansea Bay to generate renewable power and proposals to electrify the rail line between Cardiff and Swansea have both been dropped by the government.

Sweet stall owner Rachel Jones: ‘If I knew that it was going to be like this, I probably wouldn’t have turned up to vote.’ Photograph: Tom Wall/The Observer

“The overall amount of capital expenditure is being constrained because we have to pay a €40bn divorce bill for leaving the EU. People are beginning to see that some of the big promises about investment are evaporating, and that is feeding into this feeling that we are being left out in the cold again,” he says.

The city’s Brexit voters are increasing bewildered and disillusioned. Rachel Jones, who has been selling sweets from the family stall in the market for seven years, is so fed up with the uncertainty she says she wouldn’t bother to vote if she got the chance again. “I think it was a wasted vote, 110%. If I knew that it was going to be like this, I probably wouldn’t have turned up to vote,” she says over the piped pop music echoing around the cavernous market hall. “You understand it is going to take time, but it doesn’t seem to be going anywhere.”

She says she wanted to register a protest vote by putting her cross in the Leave box: “Swansea is having a really hard time at the moment. If you walk around you just see boarded-up businesses and charity shops.” But she says that now uncertainty around Brexit risks the very future of the market. “People are frightened to spend money. Things have gone up in price but wages haven’t gone up. None of us knows what is going to happen.”

Butcher Peter Mills, who voted Leave, says many people would vote differently given another chance. “I think the country would vote Remain now. Everybody is fed up – it’s gone on and on,” he says from behind his meat chiller. “I know a lot of money is coming from the EU, but whether we will have the money from Whitehall when we go out is another thing.”

One of his customers, Mal Guard, who also voted Leave, says he wouldn’t vote again. “I probably wouldn’t bother because the government doesn’t listen to Joe Bloggs in the street. They listen to their own cronies and that’s it,” he says.

Some of the clues as to why the Labour-voting city opted Leave in such large numbers can be found at Eastside food bank in the Mount Zion Baptist Church on Swansea’s post-industrial eastern fringe. Demand has grown by about 40% a year since the food bank was established in 2014. And between May 2017 and May 2018 the number of people referred to the charity by frontline professionals such as health visitors and social workers surged by about 70%.

Baptist minister Chris Lewis: ‘They think these posh idiots are leading us to disaster.’ Photograph: Tom Wall/The Observer

Chris Lewis, the Swansea-born and bred Baptist minister who runs the food bank, says the city has never fully recovered from the decline of heavy industry in the 20th century. “It is a significantly deprived area. Regeneration hasn’t really replaced the industrial base that employed people in this area,” he says as a steady stream of people come in to pick up emergency food parcels.

Lewis, who voted Remain, says many Leave voters were angry about the state of their community, which had been further impoverished by benefit cuts and austerity. “Some of it was a protest vote. They felt alienated by sort of every elitist, privileged government,” he says. “There was a degree of racism too – some people felt threatened by immigration.”

But he believes Leavers are now switching sides as the reality of a Tory Brexit dawns on them. “Some of the people who voted as a protest have flipped. They think these posh idiots are leading us to disaster in a charge of the light brigade.”

On the main shopping street in the east of Swansea, there is still considerable support for Brexit. Michelle Whitton, who works in an insurance call centre, says it is not going well but she would still vote the same way. “I’m glad I voted Leave, but whether we are going to get what we wanted I don’t know,” she says.

But other Leave voters would choose differently now. Kaywan Ahmad, who is cutting a boy’s hair in a barber’s shop in Woodfield Street, says he feels as if he was tricked. “I read on Facebook that a vote for Leave was good for the NHS. But afterwards I realised it’s bad for the NHS,” he says. “I’d vote to stay if there was another vote.”

Brexit has already hit his business. “I had about 12 Polish customers who used to work in Swansea. They would come every two weeks, but now they’ve gone back home,” he says.