AFAIK ergot is not illegal. All you need is rye seeds and patience.
Though I wouldn't recommend it, not just because the dosage is not controlled, but also because from what I have read and watched.

ergot is the nearest natural mind altering substance to LSD.

The UK law is weird in that fresh magic mushrooms are not illegal but once dried they are (ie processed). Again from what I have seen of people who have eaten, not recommended.

Personally, alcohol (4.5% ABV) is the only & most potent mind alterer for my tastes, and then sufficient to re-hydrate while dancing.

FWIW codeine is an opiate and addictive.