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Experts in Kent say the government must review drugs laws after revelations some people can get them to their door faster than a takeaway pizza.
The annual report by the Global Drugs Survey has found 37.1% of people who use cocaine can get access to it within half an hour in England and Scotland.
It comes as around one in 10 of those questioned in England and a fifth in Scotland thought they could get a takeaway as fast.
Professor Alex Stevens, a criminologist at the University of Kent, said the findings highlight England and Scotland as having some of the highest levels in Europe.
"Given that we know that Britons are among the biggest consumers of illicit drugs in Europe, it is not surprising that they're also among the biggest customers of dark websites which sell these substances," he said.
"This report shows again that the government's ambition to create a 'society free of drugs' is completely unrealistic.
"The government does not know how to achieve this aim, according to research by the Home Office itself.
"It's time the government followed the advice of countless expert groups and select committees and carried our a fundamental review of our drug laws."
Some 17% of respondents in France said they were able to get hold of cocaine in 30 minutes of less.
The Netherlands had a rate of 39.6%, 38.5% in Denmark and 34.15% in Czech Republic.