My reading is that if you only want to fly in GB in an aircraft of 2000kg or less with a maximum of 3 pax you're ok on a PMD. I understood that this was originally a Covid-related exemption expiring at the end of March 2021 but it seems to have morphed, sensibly, into permanence. I'm happy to be put right by anybody who's better read than me in the topic - I've gone for a lie-down in a dark room after trying to make sense of it.