Organised crime is far more involved in running Britain’s sex trade than previously thought, with more than three-quarters of brothels found to have links to criminal gangs, according to pioneering research. It claims that sex workers’ movements were controlled by brothels in a third of cases and criticises police for failing to tackle the criminals who control much of the off-street sex industry.

Published by an independent thinktank, the Police Foundation, the study is the first of its kind to document the links between organised crime and prostitution in a comprehensive way.

Using police data, researchers examined 65 known brothels in Bristol over two years, a figure which is a fraction of the true total, and interviewed more than 100 officials from the police and supporting agencies.

The report criticises the failure of local police to protect vulnerable sex workers, quoting one source saying that organised crime in the sex trade is “too hard [to tackle] for the amount of harm it causes”, while admitting that operations against brothel owners are rare.

The findings come shortly after the conviction of Christopher Halliwell for the murder in 2003 of 20-year-old Becky Godden, a Swindon sex worker, a development that has prompted debate about the ability of the police to provide sufficient protection to sex workers.

The cost of tackling trafficking for sexual exploitation in the UK is estimated to be £890m a year, but the study highlights a near absence of proactive police strategies. “Occasional welfare checks were completed at brothels by a local police team and partners, but sex workers rarely came forward,” it states.

“Consequently, there were few calls to respond to and little information to direct more proactive policing efforts.” It says that police welfare checks at brothels are “sporadic and not core business for any local agency”.

Researchers say police, whose organised crime work is primarily focused on theft and drug-related offenders, did not apply a rigorous approach to the issue. “While one or two officers had attempted to scan online ads for the threat of exploitation, this was not done systematically or regularly,” the report states.

Sex workers most vulnerable to trafficking are those at “pop-up brothels”, which constitute up to a fifth of the number identified and move location frequently. Almost half of the sex workers identified in Bristol are Romanian.

The combined failure of any agency to take full responsibility for exploitation in the off-street sex trade, the Police Foundation claims, is leaving many sex workers isolated and vulnerable to exploitation by organised criminals.

“The relative impunity with which pimps and traffickers operate, combined with the almost total exclusion of many off-street sex workers – particularly foreign nationals – from mainstream society, requires a radical reconsideration of what the police and other relevant agencies should be doing,”the report adds.

Overall, the Police Foundation recommends a radical overhaul of local police approaches to organised crime in the sex trade. It urges the police, working with other local agencies, to do more to help victims of exploitation to come forward and offer more protection when they do.

The study also outlines a need for police forces to gather more robust intelligence: “The police and other local agencies need to do more to identify the hidden victims exploited in the off-street sex market and facilitate investigations for which no victim comes forward.”

Although the buying and selling of sex is legal in Britain, pimping and running brothels are illegal. The International Union of Sex Workers, a trade union affiliated with the GMB, advocates complete decriminalisation as the only way to ensure that sex workers have the full protection of the law.