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Londoners are consuming more cocaine than any other European city, it was revealed today.

The capital’s cocaine market is worth an estimated £1 billion a year, and about 23kg of pure cocaine is snorted a day — equivalent to 567,445 doses.

The quantity is twice that of any other European capital, and more than that taken in Barcelona, Amsterdam and Berlin combined. But the rate consumed per person is less than that of Bristol, which came top of 75 European cities studied by King’s College London.

Forensic scientists analysed sewage water for levels of cocaine derivatives metabolised by the body. Their results, revealed by Sky News, showed cocaine usage increased by about 30 per cent at weekends. Researcher Dr Leon Barron said: “That is in contrast to other cities where you see a very marked recreational use at the weekend, and so cocaine is an everyday drug in London.”

London’s daily cocaine market is worth an estimated £2.75 million. A gram costs about £40. Experts say the purity has increased from below 10 per cent to about 30 to 40 per cent, meaning users are more likely to get addicted.

Lawrence Gibbons, the head of drugs threat at the National Crime Agency, said: “I think people don’t want to go back 10 years when purity on street level was down to three to five per cent.”

Last month the Office for National Statistics revealed there were 637 deaths from cocaine overdoses last year, up 158 per cent since 2014.

Met Commissioner Dame Cressida Dick has blamed middle-class cocaine users for fuelling the drugs trade and the capital’s knife and gun crime.

Mayor Sadiq Khan has said drugs are “a key driver for the levels of violence on the streets”. There have been more than 1,000 drug-related search warrants issued to the Met since April last year.

Mr Khan said: “Recreational drug use is not a victimless crime, and anyone purchasing illegal drugs should be under no illusions about the horrific exploitation in the supply chain.” London’s consumption of its “most popular Class A drug” doubled from 2011 to 2015, but fell more recently.

Tony Saggers, the NCA’s former head of drugs threat, told Sky News: “I would say London has got to the point of [market] saturation. The demand has gone up, the price has stayed stable, people are able to lay their hands on it freely… but other cities are catching up.”

This saturation explains why gangs have turned to “county lines” networks to export the drug to provincial towns.

Cocaine is imported from countries such as Colombia, and has been found hidden in fruit shipments. More international crime networks have entered the market, making it more competitive.