There's lots of old-time-radio (OTR) downloads available here (including "Omar" should you feel like setting up a discussion group talk about its literary merits in depth!)
Science fiction your bag? Try "The Seeing Ear Theatre"....even though they're American they've made an effort to spell theatre right and they do a damned good drama! Then of course there's that old classic "The War of the Worlds" with Orson Welles
Moving swiftly along to the weird and wonderful (usually vintage jumble sale type material)...and you can't do better than the "365 days project". As suggested by the name a new gem is posted each day this year. The parent site is worth a look too.
Look, there's loads more and not just audio......but I'll wait to see whether anyone is interested before I post the links