More than 300 slot machine adult gaming centres are running 24 hours a day on Britain’s high streets, despite warnings of the risks they pose to vulnerable gamblers.

Two of the leading slot machine operators – Merkur and Admiral – have opened dozens of new around-the-clock outlets in empty retail units across the country over the last few years. The two firms operate more than 500 venues across Britain, with most now open 24 hours a day.

In many cases, local residents vigorously opposed the venues opening, but council planning committees failed to block the applications. Campaigners are now calling for a crackdown on the sector’s expansion.

Nick Harvey, from the charity Gambling with Lives, which supports families bereaved by gambling suicide, said the rollout of 24-hour slot machine venues had been “under the radar”. Campaigners want to see new powers to allow councils considering applications to assess the cumulative impact of gambling.

Harvey said: “Slots venues contain the most addictive gambling products out there, causing misery to communities while bringing little to no economic benefit to the local area.”

This weekend, in response to Observer figures, the Association of Directors of Public Health and the Local Government Association called for new powers for councils to halt the “proliferation” of 24-hour slot machine centres in some towns.

The concerns raised over the rapid expansion of the sector come as the Gambling Commission prepares to publish its research on gambling harm this week. Preliminary findings published last year found that 2.5% of the adult population may be suffering from problem gambling. The commission has previously put the proportion of people suffering from a gambling problem much lower, at 0.3% of adults in Britain.

At a Greenwich council planning committee meeting on Tuesday, members considered an application for a new 24-hour Merkur Slots centre in Eltham, south east London. There were more than 60 objections from residents as well as an open letter from Labour councillors Lauren Dingsdale and Sammy Backon, who wrote: “Allowing planning permission for this premises would encourage vulnerable individuals to gamble more than they can afford.”

Separately, a police officer wrote that he had seen multiple police logs of customers at Merkur venues “criminally damaging gaming machines after losing money and in some instances threatening and/or assaulting staff”.

Councillors refused the application, but Merkur has already lodged an appeal because the local authority had not reached a decision within the statutory eight weeks.

Merkur operates 24-hour slot machine centres across the UK. The company, founded by German businessmanand slot-machine tycoon Paul Gauselmann, increased revenues by 17% last year to £202m.

Former slot machine addict Tracey, 62, from Watford, who asked to give only her first name, received a three-year prison sentence in 2020 for stealing £70,000 from her employer to feed her gambling addiction.

“I would take a cab from my house to the Merkur [venue] in Watford at 5am,” she said. “I could easily spend £2,000-£3,000 in a single visit.” Tracey, who now counsels other addicts, claimed: “There’s no duty of care. You become a favourite customer because you’re out of control.”

The slot machines with the biggest payouts are known as B3 machines. These have a maximum stake of £2, but a spin speed for each game of two-and-a-half seconds. It means it is possible to stake hundreds of pounds in hours.

One former customer, who asked to remain anonymous, said he turned to slot-machine centres after participating in self-exclusion schemes at betting shops and casinos. “I went into several Admiral and Merkur venues last year,” he said. “It’s ridiculous to say the £2 limit is any kind of barrier. I lost over £1,000 very quickly.”

The last government proposed loosening the rules for slot machine operators, permitting the use of debit cards on machines and for operators to increase the proportion of B3 machines in arcades and bingo halls from 20% to 50%. An Observer investigation this year raised questions over the way centres are regulated.

John Bollom, president of the British Amusement Catering Trade Association (Bacta), described adult gaming centres as “popular entertainment venues” which are “among the safest places to gamble”. He said customers are supervised by experienced staff “well trained to spot signs of problems and provide support”.

He added: “The gaming machines in these venues are low-stake and highly regulated by the Gambling Commission, and strict age checks are enforced. [The centres] are a valued part of the high street and an essential component of the night-time economy.

“A small minority of players can have problems, and we are committed to ensuring the highest possible standards of social responsibility and that help is offered to players if needed.”

An LGA spokesperson said: “Problem gambling can lead to spiralling debt, homelessness, and relationship breakdowns. Councils have long called for more legal powers to approve or reject applications for new gambling premises, especially when there is a proliferation in a small area or on a single street.”

The Department for Culture, Media and Sport said it was “committed to reducing gambling-related harm”. The Gambling Commission said councils can impose conditions including reducing hours if gambling is not being provided in a way that is fair and safe. All adult gaming centres must identify customers who may be at risk of experiencing harm and interact with those customers.

Admiral and Merkur Slots have been approached for comment.