Last month, in a private meeting, Brian Iddon, Labour MP for Bolton South East, put the question to Home Office minister George Howarth.
"The minister told me that 1.5 million people in Britain use cannabis, which surprised me," said Mr Iddon, who believes cannabis should be decriminalised.
"I know that many believe the number to be more than twice the Government estimate. However, I was assured that this was the best and most up-to- date calculation. The Home Office based this figure on a 1996 survey of 9,000 people from a broad spectrum of social classes," he added.
But a careful review of the official statistics reveals the implausibility of the Government's estimate. The most recent figures for the amount of cannabis seized by both the police and customs are 13,871kg (13.6 tons) of dry plant matter and 44,607kg (43.9 tons)of resin.
The total - 58,478kg - is accepted by customs and police intelligence sources as representing, on average, 10 per cent of the total amount in circulation.
The police calculate that it is possible to roll four joints from each gram of cannabis. Therefore, over a full year, 526,302kg of cannabis will be consumed or 2,105,208,000 - 2.1 billion - individual joints.
This, in turn, means that every day, throughout Britain, 5.7 million joints are lit and that for the Government's estimate to be correct, each of the country's 1.5 million cannabis smokers would have to puff their way through 27 joints a week, every week of the year.
The correct appraisal of cannabis use is far more complicated than the Government would have us believe. While it is true that a minority of users smoke as many as 27 joints a week and more, the vast majority use the drug intermittently. Many only smoke at weekends, others once a month or less frequently - no one can tell for certain.
However, the number of individuals who indulge in one smoke or more in the course of a year in Britain is most likely to be at least three times as many as the number the Government claims.