When the Government opted to reclassify cannabis as a Class C rather than Class B drug in January 2004, this newspaper cautiously supported that move, provided that the medical evidence was kept under constant review. To that extent, there can be no objection to Charles Clarke, the Home Secretary, asking the Advisory Committee on the Misuse of Drugs to look again at this matter and to consider whether different types of cannabis might merit different classifications.

It is important, though, that the medical aspects of this investigation are free of any political element. Recent studies on the behavioural aspects of cannabis use conducted at the University of Otago in New Zealand and at Maastricht University, while not wholly original, add fresh weight to an existing and important field of research. Ministers could also hardly ignore a striking new analysis by the Dutch authorities which implies that certain varieties of “skunk” are considerably more potent and dangerous than standard cannabis resin. If this expert committee concludes either that the reclassification has been superseded by events or that a division should be made in the legal status of cannabis, the Home Secretary would be well advised to take that counsel seriously.

It is not, however, the only aspect of this issue that should be considered. Two forceful arguments were originally put forward in favour of reforming the old law on narcotics. The first concerned the balance of evidence of the harm associated with cannabis. The second related to the amount spent by the police in chasing people whose principal “crime” was putting themselves at potential risk and who were otherwise law-abiding citizens.

A comprehensive review of cannabis policy has to look at how the reclassification has been pursued across police forces, what needless inconsistencies have occurred as a consequence and whether admittedly often anecdotal suggestions that much time has been saved through a less rigid approach to cannabis and those who use it are in fact true.

If a fundamental review of the evidence implies that cannabis is considerably more of a threat than previously believed, the medical aspect of this debate will have to be awarded more weight than the impact of reclassification on policing. The strong suspicion, however, is that the medical debate will not be resolved so clearly. There will be heated discussion on the effects of cannabis on those using it at a particular level of intensity over a long period. Even if a consensus could then be reached, a doubtful assertion, argument will still rage over whether the effect of cannabis is truly equivalent to that of other Class B drugs, or indeed to items such as alcohol or tobacco which have not been criminalised.

Mr Clarke has kicked this controversy into the long grass. The review he has commissioned will not even start until almost a month after polling day. He should make it clear, nonetheless, when the issue re-emerges, that every implication of any attempt wholly or partly to reclassify cannabis will be examined before implementation.