Estimating the proportion of UK drug consumption which is imported on the basis of customs and police seizures for particular drugs

In this paper it is proposed that the ratio of the amounts of a particular illicit drug seized by Customs to those seized by the Police in a particular year is linearly related to the proportion of total consumption which is imported. In the model proposed, the constant for the linear relationship is calculated for drugs known to be almost completely imported (cannabis, heroin and cocaine). The constant is then used to estimate the percentage importation for amphetamine. Prior to 1990, the calculation indicates that around 20% or less was imported whereas the levels in the past 4 years have been much higher. These results are in excellent agreement with data provided by the amphetamine profiling project, which shows that, in 1993 almost 90% of amphetamine had been imported. It is suggested that the model could be used as a broad indicator of the percentage importation of other drugs from the level of Customs and Police seizures. A more refined model would be needed for more precise measures, but these are not always needed for intelligence purposes. Equally it could be argued that an improved model would be limited by the vagaries of the available data.