Flynn was a "a titan in the UK drug law reform movement" according to the Transform Drug Policy Foundation, a think tank of which he was a patron. This involved asking numerous oral and written parliamentary questions at the request of Transform, tabling early day motions and private members bills, hosting events in Parliament on behalf of the charity, as well as doggedly raising the issue of drug law reform in the house in a series of memorable barnstorming speeches. His speeches included objecting to the classification of psilocybe mushrooms as illegal in the Drugs Act of 2005, in which he said: "We cannot make nature illegal.
Flynn's advocacy for drug law reform was characterized by his active engagement with the UK parliament, including questioning lawmakers, proposing legislation, organizing events, and delivering passionate speeches to raise awareness and push for changes in the legal framework surrounding drugs.