Prostitution and illegal drugs are contributing around £10bn a year to the British economy, data from the Office for National Statistics (ONS) has shown.

These underground activities are worth 0.7% of GDP, which is roughly the same proportion as agriculture, gambling and accommodation services, including hotels, bed and breakfasts and caravan parks.

They are worth more than the advertising industry, which makes up 0.5% of GDP, and double the contribution made by real estate activities.

Prostitution makes the largest contribution – around £5.3 billion – while illegal drugs fall only slightly behind at £4.4 billion, a report by the ONS revealed on Thursday.

Graeme Walker, head of national accounts at ONS, said:

“In terms of the new concepts coming in, illegal activities is the biggest. For the rest of GDP we do things like sending questionnaires to businesses, asking them how much they have earned.

“We don’t think it would be right to directly collect information on illegal drugs and prostitution and we have no plans to contact people involved in these activities.

“We think our data fits the purpose for giving people an idea of the size of illegal activity.”

The ONS say the figures are “based on a variety of sources and assumptions” but add that there are “significant limitations in the availability of data.”

The contribution of prostitution was calculated using a number of estimates, including the clients per prostitute per week based on Dutch practise, the average price per visit and the cost of room rental and clothing.

Meanwhile, the cost of drugs contribution was calculated using estimated figures based on sales, import price, value, street price and number of users.

Other illegal activities such as the smuggling of alcohol and tobacco into the UK are already included in GDP and make up around £300 million.

Photo by Christian C