As I recall, (not that I'd know anything about this subject ) philocybin tends to grow on untreated pastures on hillsides, particularly in wetter cooler places, such as Dartmoor, Wales, Scotland, and rather well at Beaconsfield Rugby Fields.
It is psychoactive, and use of it tends to lead to hysterical laughter, giggling fits, and mild hallucinations. (so I'm told by ashamed former lawbreakers). Best way to identify philocybin is apparently make a tea from it and see what happens when you drink it. Sounds quite awful, quite right its banned. Its much more sensible to stick to legal stimulants such as nicotine and alcohol, the only side effects they have are lung cancer, heart disease, violence and liver sclerosis; so much more sensible to use.
As I woudnt expect to find Magic Mushrooms in a forest, perhaps the police are actually looking for gangs, harvesting all the wild mushrooms to sell for huge sums to fancy restaurants. It devastates the ecology and should be rightly be clamped down on. Presumably wholesale clearance of forest fungi for commercial gain is illegal, but not sure what exactly the laws and penalties are.
In my experience (of what I've heard, not first-hand), penalties for hippy-type plant & fungi stimulants are not ruthlessly enforced with custodial sentences, there is a degree of tolerance and hand slapping for minor use, eg verbal warnings or small fines.