I found a neat comprehensive little list of psychoactive mushrooms (other than Amanita Muscaria) that can be found in the UK, that have notable potency:
- Psilocybe Semilanceata (the most commonly hunted I think)
- Psilocybe Montana
- Psilocybe Coprophila
- Psilocybe Cyanescens
- Panaeolus Foenisecii
Unfortunately we don't allow mushroom ID'ing or hunting questions on this forum because we consider ourselves unequipped to help you make distinctions between the mushrooms you are looking for and similar-looking but inedible or toxic ones.
I strongly recommend that you buy a mushroom book such as the one in the River Cottage series (I have that) which is meant for the UK, which lists mildly and strongly toxic ones so that you can learn to avoid those. That book is meant to help you find gourmet mushrooms instead of psychoactive ones though so there might be better suited books out there.
In any case, also find keys (ways to determine the species) on the mushroom species I listed above.
Then divert to a site like The Shroomery (shroomery.org) to help you with the rest, like ID'ing ones you found.