* The most common forms of cannabis are Moroccan (soap bar) resin (also known as hashish) and skunk. Soap bar has a potency of 3 to 7 per cent THC (tetrahydrocannabinol, the psycho-active chemical in cannabis that makes you high); skunk's THC content is between 8 and 20 per cent.
* In poorer neighbourhoods, skunk is the only cannabis available and is often adulterated with heroin, crack and cocaine.
* Most of what is called skunk is high-strength cannabis. Hydroponically produced and domestically grown, it sells for between pound;20 and pound;25 for an eighth of an ounce, which could easily be smoked in one night.
There is another variety, also called skunk, whose street value puts it well beyond the means of most young people.