There are many varieties of mushrooms or psilocybin (magic mushrooms) in the U.K. There are over 40 hallucinogenic species in the genus psilocybe, a few of which can quite easily be found in the U.K. countryside. Nearly all of the psilocybin containing mushrooms are small brown or tan mushrooms easily mistakable for any number of non-psychoactive, inedible or poisonous mushrooms in the wild. The primary distinguishable feature of most psilocybin containing mushrooms is that they bruise blue when handled.

Mushrooms contain several active alkaloids, the most common being psilocybin, psilocin and baeocystin. When taking mushrooms for recreational purposes you must be aware of the dosage and consider the individual species and it's strength. Five grams of dried out mushrooms is a high dosage, first time users should start on one to two grams.
Once they have been indigested, the mushrooms will take around an hour to take effect. Mushrooms will give you the feeling of energy, and a sense of restlessness, (often resulting in long winding walks). Laughter is very common, and can last for a number of hours. There is a light trippy experience (this will be stronger if you exceed the stated dose) where lights and images can be exaggerated. Lots of people experience vomiting and nausea, as well as unwanted thoughts and visions. Mushrooms can be a strong psychoactive experience, especially when taken in high doses. Mushrooms aren't addictive, or likely to cause psychological dependence. If you suffer from mental, psychological or emotional problems you should avoid taking mushrooms.

Psilocybe mushrooms have been widely used by Native Americans in Central and South America. As the Europeans began to discover the world, the first use of mushrooms was recorded in the 16th Century. Once the active ingredient of the mushroom was isolated (psilocybin) it began to attract a western following. By the 1960's mushrooms had become freely available as a recreational drug.

In the U.K. magic mushrooms are classed as a Class A drug and are illegal.
This applies to most other counties.