· There are three sub-species of cannabis plant - Cannabis sativa, Cannabis sativa indica and Cannabis sativa ruderalis - but it is the indica sub-species that provides the majority of the world's skunk, hash, kif or marijuana. The key components of the drug are THC (delta-9-tetrahydrocannabinol) and CBD (cannabidiol).

· After cannabis is smoked, the THC acts on cannabinoid receptors in the brain, affecting memory, concentration, and perception and movement. The effects last three-to-four hours.

· Cannabis costs anywhere between £55 and £134 per ounce.

· Last month, a study by the Beckley Foundation found cannabis is less harmful than both alcohol and tobacco.

· The use of cannabis by humans has been traced back as far as the Mesolithic period (around 10,000BC).

· Queen Victoria was prescribed cannabis to calm period pains.

· 1936 saw the release of over-the-top anti-marijuana film Reefer Madness.

· Indian tradition says the gods sent man cannabis so he might attain delight, courage and heightened sexual desires.

· There are thought to be 140 million cannabis users globally (about 2 per cent of all people), making it the most popular illegal drug.