Prostitutes cost France €1.6 billion every year

France's 37,000 prostitutes are costing the country to the tune of €1.6bn euros every year, according to a new study which aims to "reverse the myth that sex work generates sustained growth".

While prostitution in France brings in an estimated annual turnover of €3.2bn, with French sex workers making an average gross total of €87,700 a year, much of this sum is sent abroad, rather than filtering back through the French economy, according to the study funded by the European Commission.

The study, by Le Mouvement du Nid, which actively campaigns against prostitution, also claims that there is serious tax evasion on these earnings, totalling €853m a year, while the rest of the figure is made up by the indirect social costs associated with prostitution, such as imprisonment for pimping, health expenses and drug addiction.

The report authors state: "If the clients of prostitutes were to spend their money on any other activity, France would increase its tax revenues and save several hundred million euros each year from prostitute-related expenses."

In recent years, European economies have started to include the revenue generated by so-called "shadow economies" such as prostitution and illegal drugs, as part of new regulations introduced by the European Union to better estimate a country's GDP. But there appear to be few reports on how much the industry drains a nation's economy.

Prostitution added around £5.65bn (€7.8bn) to the UK economy in 2013, according to figures released by the Office of National Statistics last year, leading some commentators to suggest that UK prostitutes should be taxed.

The ONS estimates that each of the UK's estimated 60,879 prostitutes had around 25 clients a week in 2009, at an average rate of £67.16 (€94.16), although the study acknowledged the difficulties in accurately measuring such a secretive and hidden industry.

According to official Spanish government statistics released last year, prostitution and narcotics account for nearly $12bn (€11bn) of the country's total GDP, almost 1% of the total Spanish economy. In Germany, prostitution and illegal drugs generated $91bn (€83bn) in 2013, although it is unclear how much of this sum is lost due to social costs or due to the money being sent abroad.

Maîtresse Gilda, a spokeswoman from the French sex-workers union Strass, branded the study "delusional" and "insane", highlighting the difficulties for any country trying to accurately estimate the industry's worth.

"This isn't a scientific study," she said. "The arguments aren't substantiated. Not only does it belittle us, but it puts the economic and social burdens on our shoulders."

"How can they know the number of prostitutes in France?" she continued. "This is an industry where everything is secret and opaque. The numbers are insane," she added.

Earlier this year, France's Senate rejected a planned law that would penalise people wanting to pay for sex, instead choosing to maintain the offence of soliciting.