I have a three metre tall Cactus, which I now have to reduce somehow! It consists of two three metre cactus and two 1/2 metre cactus and I really would like to know if I can cut the two three metre sections to a much more manageable height? Not sure if this is possible.
This depends greatly on the type of Cactus that your are growing.
Here is a link that gives an over view of pruning Cactus.