Professor Alex Stevens:

As far as I am aware, that list has been abolished, partly because of the difficulties of enforcing it and partly because of the arbitrariness that any such list is bound to employ. Take, for example, somebody who uses heroin. If I were to use heroin, the effective dose would be very low indeed because I have no tolerance to heroin. I do not use it regularly. If a person who uses large quantities of heroin every day used the amount that might even kill me, it would have very little effect on him or her because he or she has higher levels of tolerance. To have the same arbitrary weight limit for me and that person seems rather strange because it depends on the person who is taking it. Any weight threshold is bound to be arbitrary. There is that issue. There is the difficulty for the police officer of determining, by eye, what the weight is on the street. There is also the inevitable inequity between substances. This is another area that my colleague, Dr. Caitlin Hughes, has worked on. If one has different weight limits for different substances one would hope that there was some relationship between the weight and the harm, but the research Dr. Hughes has done on various international systems which include thresholds shows wide disparities between the amount of doses that are covered and the harm that would be covered by different thresholds for different drugs. As a result of the inevitable arbitrary nature of setting a weight threshold, I prefer a model which places that evidentiary burden on police and prosecutors to prove that a person has intent to supply rather than merely reading it off the weight of the substance.