The Forager’s Association has a list of other people who run foraging courses all over Britain:
Several organisations take specialist interest in various aspects of the natural world, but with varying and sometimes discouraging opinions on the innocent pastime of foraging. Most of them contain both an amateur and an academic wing. Their websites are largely open to all and full of information.
Botanical Society of Britain & Ireland https://bsbi.org/
British Mycological Society https://www.britmycolsoc.org.uk/
British Phycological Society (Seaweeds!) https://brphycsoc.org/