Published: 04:46 EST, 28 May 2014 | Updated: 08:02 EST, 28 May 2014
London could have the highest levels of cocaine use of any city in Europe, a new report suggests.
Researchers tested the amount of a number of illegal substances in the waste water of cities across the continent in a bid to assess Europe's drug habits.
They found London had the highest levels of cocaine of any of the 42 cities tested, well above that of other capitals including Amsterdam and Paris.
London's sewage water contained 711mg of benzoylecgonine, the main chemical in cocaine, per 1,000 people, compared to 393 in Amsterdam, 243 in Paris and 233 in Milan.
Levels in London's water were nearly double those recorded in a similar study two years ago, results show.
The study, by the Lisbon-based European Monitoring Centre for Drugs and Addiction, also highlighted an apparent East-West divide in drugs used.
While the populations of cities in Western Europe were more likely to cocaine, ecstasy and cannabis, Eastern European citizens are more likely to be developing a crystal meth habit.
The research shows how levels of drugs in waste water rise and fall over the week.
In London, the amount of cocaine in the water increases to 904mg on Saturday, compared to a 799mg average on weekdays.
The amount of crystal meth in the capital's water trebles on a Saturday and levels of ecstasy jump from 27mg per 1,000 people on a weekday to 69mg on a Saturday.
Prague had the highest levels of crystal meth in its water, at 327mg per 1,000 people, the Czech city of Budweis the second highest and Bratislava in Slovakia the third highest.
Cannabis appears to be the drug of choice in France and southern Europe, with the highest levels recorded in Paris, Barcelona and Athens.
UK government statistics state that around one in 12 adults used illegal drugs in 2012, but only one in 50 took Class A drugs like cocaine.
Following the publication of the research, Marcus Roberts, chief executive of charity DrugScope, warned cocaine users about its dangers.
Mr Roberts said: 'While government data shows that powder cocaine use been falling since 2008/09, it remains the second most commonly used illicit substance in the UK.
A new study of water across Europe suggests London has the highest cocaine use of any of the cities tested
'But it is a harmful drug and users should be aware of the risks. Cocaine is a powerful stimulant which may place strain on the heart.
'When taken in large doses, people can experience extreme anxiety, paranoia and hallucinations and regular use can lead to dependence.'
But London's worrying position as the continent's cocaine capital was today played down by the Home Office, which criticised the new research.
Crime Prevention Minister Norman Baker has played down the research, insisting drug use in Britain is falling
Crime Prevention Minister Norman Baker said: 'Waste water analysis is an emerging and as such unproven technique for measuring the prevalence of drugs.
'Studies in the UK, including figures from the independent Crime Survey for England and Wales, show that drug usage remains at its lowest level since records began in 1996.
'We will however continue to review new ideas and techniques as they are developed to ensure the UK has robust systems in place to measure and track drug prevalence.'
The report's authors have defended the research, stating: 'Waste water analysis provides the possibility to collect and report measurements more quickly and regularly than is the current norm for national surveys.
'If used more routinely as a complement to other European drug surveillance methods, it has the clear potential to shed extra light on drug use trends in Europe, including the use of new psychoactive substances.'
Some experts have suggested the methods can actually be more accurate than studies based on questionnaires because those answering surveys are not always honest.