“People are appalling at knowing how their drug use compares to other people,” he said. “My favourite statistic from last year was 20 per cent of people who were alcohol dependent using the World Health Organisation screening tool thought their drinking was average or less than average.”

Nearly 40 per cent of people who had been asked about their drug use by their GP either lied and said they never used drugs, or downplayed their use. About 22 per cent of alcohol drinkers did the same.

The survey is being launched in Australia today, but will also be run in the US, in partnership with NBC, and in the UK, with The Guardian, Mixmag and the Gay Times.

Dr Winstock said he created the project to capture a broader snapshot of drug use than is usually available.

“Most governments are interested in drug use patterns among the sickest and most disadvantaged,” he said. “But that represents a fraction of the people who use drugs”.