Heroin dealers and users stood a lower chance of being convicted in 1989 than they did in 1985 - despite 40 per cent more being spent on drug enforcement.
Given the Government's demands for 'value for money', both police and Customs should be made to justify the pounds 335m spent on drug enforcement, Professor Alan Maynard, one of the study's authors, said.
'Throughout the 1980s the chief response to the perception that Britain had a rising drugs problem was to invest more in anti-drug enforcement activity. But on the data that is available there is no evidence this has reduced the size of the illegal heroin market,' he said.
'Customs rarely achieved the 10 per cent seizure rate which they regularly claim in the press, while after 1985 the proportion of heroin seized by the police fell from 1 per cent to around 0.3 per cent.'