It’s pitch black and we’re crawling along a secret underground tunnel beneath a high street in Hull. We pass rotting beams propped up precariously by stacked breeze blocks. A rusty car jack is helping prevent the shop floor above from falling in.

Through the rubble, we follow a Trading Standards Officer, his torch swinging back and forth in the darkness until it rests on a hidden stash of thousands of illegal cigarettes.

This is just one such surreal experience while investigating the sale of illegal cigarettes in Hull. In one week we repeatedly witnessed counterfeit and smuggled tobacco being sold in high street mini marts – and were threatened by shop workers who grabbed our cameras when we tried to film them.

This is now a familiar story being repeated across Britain. In April, the National Crime Agency (NCA) raided hundreds of high street businesses, many suspected of being supplied by international crime gangs. Trading Standards teams have also found a thriving trade in illicit tobacco.

One leading criminology expert called the networks behind the supply of illegal cigarettes the “golden thread for understanding serious organised crime”, because of its links to people trafficking and, in some cases, illegal immigration.

So, in some ways, these high street shop fronts connect the various domestic problems facing Britain today.

Political researchers claim it’s also damaging trust in police and the government – and turning our high streets into symbols of national decline.

Alan, a former detective and now a Trading Standards officer, searches for counterfeit and smuggled cigarettes sold under the counter in mini marts, barber shops and takeaways around Hull, which he says have spread across the city at an alarming rate.

Under the floorboards of a mini mart called Ezee Shop, a network of these secret tunnels hide contraband stock. As battered suitcases and black sacks stuffed full of cigarettes are heaved up through the makeshift trap door, a man who we’re told helps out in the shop watches on laughing.

“It’s not something dangerous, it’s only cigarettes,” he says. “Everywhere has it; barber shops, takeaways.” Some shops, he adds, are selling drugs including crack cocaine.

Alan estimates that there are about £20,000 worth of illegal cigarettes in this haul, a tiny proportion of a crime that HMRC says costs the country at least £2.2 billion in lost revenue.

Today’s raid won’t change what’s happening on Hull’s high streets, he says. He has been to some shops at least 20 times and he estimates that there are some 80 shops selling illegal cigarettes in the city.

“We’re losing the war,” he says.

He has been with Trading Standards for many years but didn’t want to be fully identified because he’s worried about the organised crime gangs often supplying these shops.

It’s not long before someone claiming to be Ezee Shop’s owner turns up. Alan says he is a Kurd from Iran. He is furious with us filming his illicit stock being taken away.

Some of the illegal cigarettes sold across Britain are made in this country. Others are produced cheaply in countries like Poland or Belgium. Some are designed to imitate established brands. Illegal cigarettes are sold without the necessary taxes and duties, and many do not conform to safety standards.

Previously the Local Government Association warned that some black market cigarettes contained “human excrement, dead flies and asbestos”.

We went undercover, visiting 12 shops in Hull, some multiple times, to try and buy these cheap cigarettes, and secretly filmed the responses.

The windows of many of these shops are covered with large pictures of fizzy drinks, sweets and vapes, obscuring what’s going on inside.

Nine sold us illegal cigarettes and hand-rolling tobacco. Two told us where we could buy cheap packs. We were openly offered a selection of brands with packets costing between £3 and £7 – instead of the average UK price of about £16.

None of the businesses we bought illegal cigarettes from in Hull responded to our request for a comment. But this is not only a Hull problem.

Data shared with the BBC from investigators working for an international tobacco company say that last year they identified more than 600 shops selling illegal packets, with several cities including Bradford, Coventry and Nottingham flagged as hotspots. The BBC is unable to verify these figures.

In Bradford alone, they say they found 49 stores selling fake products in just two days. In the end, they had to stop the test purchases because they didn’t have enough test bags to put the items in.

All of this is a growing problem – but it is also one with specific causes: profits, a lack of resources to enforce the law, a complex criminal supply network and in some cases organised immigration crime.

Professor Georgios Antonopoulos, criminologist at Northumbria University Newcastle, believes money is at the heart of it. “Legal tobacco products in the UK are subject to some of the highest excise taxes in the world,” he says.

Illegal cigarettes are sometimes sold for as little as £3 to £5 per pack – compelling for some customers during a cost of living crisis.

In some cases, the financial penalties issued to criminals may be much lower than the profits they can make.

In the case of Ezee Shop in Hull, the shop owner had been convicted for selling illegal cigarettes in the past and was fined £80, plus costs and a £34 victim surcharge.

Tougher rules introduced in 2023 mean those convicted now can face higher fines of up to £10,000 – but this may still be lower than the value of the stash.

After the raid, we went back to the shop, covertly. Within a few hours it had reopened, restocked – and was selling illegal cigarettes once again.

Leading criminologists tell the BBC that UK authorities are struggling to deal with the problem.

Prof Antonopoulos says teams are “chronically underfunded”. He claims that police prioritise violent crimes and drug trafficking – “which is understandable,” he adds.

Some Trading Standards officers are frustrated with the powers available to them. “The general public don’t understand why they can’t be closed down,” Alan says.

They can use anti-social behaviour legislation to close shops for up to three months – but it can require statements from other businesses and members of the public.

We were told that after some shops shut down, the criminals simply reopen nearby. Alan wants a ‘three strikes and you’re out’ policy to permanently close law-breaking businesses.

Last year, the previous government provided £100 million across five years to support HMRC and Border Force to tackle the illicit tobacco trade. But since then, the Chartered Trading Standards Institute warned that some broader forms of organised crime – including scammers and rogue traders – could effectively become decriminalised, due to a lack of funding.

As for the suppliers, HMRC says there are so many organised crime groups operating across borders that it is hard to limit the flow of goods into the UK.

In May, Hungarian authorities raided a factory where they found warehouses full of fake cigarettes. And there’s even production in Ukraine, according to legitimate tobacco firms, with authorities there stretched because of the war.

There is also a “significant production” of illicit tobacco here in the UK, says Prof Antonopoulos.

A Trading Standards team in south Wales told us that counterfeit hand-rolling tobacco is often sold cheaply. They claimed that some of it was made using forced labour, controlled by Chinese gangs.

Dave McKelvey, managing director of TM Eye private investigators, which works with tobacco firms to gather evidence on the illicit trade, claims that Fujian-based Chinese triads operate a “vast business” here in the UK.

And trying to track down the people in charge of these criminal enterprises is a challenge.

Trading Standards told the BBC that those named as the company director often have no real involvement in the company. Instead, they may be paid a small sum each month to be listed as the director on official documents.

Later this year, Companies House will receive new powers to better identify business owners.

Authorities are trying to clean up British high streets. Just this year, we joined dozens of raids led by the NCA in barber shops and mini marts, in a month-long operation.

But the former senior detectives who worked with the BBC’s undercover team said they need more time to fully expose the organised crime supplying some of the shop fronts.

Throughout our time with Trading Standards in Hull and in the dozens of raids we’ve been on with police in Shrewsbury and across Greater Manchester, officers claimed that tobacco operations are often staffed by Kurds from Iran and Iraq. Some may not have had the right to work.

In Hull, Alan believes that some people working in the shops he visits may be recruited from asylum seeker hotels. “They’re expendable, if they get caught they just replace them with another.

Rochdale Trading Standards has made similar observations.

Criminology professor Emmeline Taylor argues that these criminal supply chains behind the supply of illegal tobacco are linked to other forms of crime – and the damage can’t be underestimated.

“They’re not just dealing in tobacco,” she says. “It’s firearms, it’s drugs, it’s people trafficking, it’s illegal immigration.”

The Home Secretary, Yvette Cooper, told us it is a “total disgrace” that “criminal gangs are trying to abuse our high streets by using shops as a front for organised crime”.

She also accused gangs of “undermining our border and immigration systems by employing illegal workers”.

Of course, there have long been pockets of criminality on the UK high street. But now experts tell us that this illicit trade is harming people’s trust in authority – and, at a basic level, their sense of fairness.

“If you’re a law abiding business following the rules, you’re jeopardising your own livelihood and the viability of your own business,” argues Prof Taylor. “And to me that’s not fair that someone can succeed by not playing by the rules.”

Josh Nicholson, a researcher at the Centre for Social Justice, believes that perceptions of crime are worse than ever. “From research we have done there is a feeling of powerlessness, a lack of respect for authority like the police,” he says.

“Are the police… seen to be tackling low level offences? When they don’t see it tackled, people’s perception is that things are getting a lot worse.”

And people tend to trust the government less when they think access to good shops has declined in their area, says Will Jennings, a political science professor at the University of Southampton, based on studies he has done.

Nick Plumb, a director at the Power to Change charity, says his research shows that declining high streets boosts support for parties that were once considered outside of the political mainstream.

“Reform UK, for example, is doing better in places with declining high streets when compared to the rest of England,” he says. “There’s a sense that … mainstream politics, local authorities have all tried to tackle this issue, and [residents] haven’t seen any change. It’s that sense of ‘the status quo hasn’t solved these things, and therefore we want to try something new’.”

Ultimately, what people see in the places they call home matters.

“People find a sense of local identity in the quality of the streets where they’ve grown up,” adds Mr Nicholson.

“When the quality … dramatically declines, and they feel they can’t even go there – what that does to a sense of community is unquantifiable.”

Additional reporting by Phillip Edwards.

Top Image credit: Javier Zayas Photography/ Getty Images

BBC InDepth is the home on the website and app for the best analysis, with fresh perspectives that challenge assumptions and deep reporting on the biggest issues of the day. And we showcase thought-provoking content from across BBC Sounds and iPlayer too. You can send us your feedback on the InDepth section by clicking on the button below.