I don’t listen to an awful lot of radio fiction these days, but there are a handful I love:
Chickenman - Spoof/homage of old-time adventure serials. Episodes are very short.
Tom Stoppard did a bunch of radio plays back in the day. Particular favourites are Albert’s Bridge and If You’re Glad I’ll Be Frank
It never technically ran on the radio, but it played a radio show on podcasts : Thrilling Adventure Hour
I find Bragg’s faux naivete too annoying to get on with In Our Time, but I do love a bunch of other Radio 4 stuff:
I’m Sorry I Haven’t A Clue - extremely long running quasi-improv panel show. Origin of the game Mornington Crescent.
The Infinite Monkey Cage - science and comedy discussion show hosted by Brian Cox and Robin Ince.
From Our Own Correspondent - Little vignettes from foreign correspondents around the globe, every week. Some if it is about the stuff that’s in the headlines, some of it is more obscure.
BBC Radio does a good line in one off history documentary series :
A History Of The World In 100 Objects: Using 100 artifacts from the British Museum to tell stories about life from across the span of history.
Germany: Memories Of A Nation: Takes a similar approach to German history, but with things actually in Germany.
US public radio can be pretty good too:
This American Life - Come on, if you’re in this thread, you know what this is.
Radiolab - Science related oddities
More Perfect - I think this airs on the radio. It’s definitely a podcast. Anyway, it’s a fascinating show about the Supreme Court.