Undone

Strange is good

—Edna Turner, Undone

At three series (2006-2010), this is the longest-running comedy drama made especially for BBC Radio 7. Undone tells the story of Edna Turner, and her new job in London. When she arrives to work for "Get Out!" Magazine, she discovers that there is a weirder version of London, called 'Undone'. She is given a second job, to patrol the gaps between, and stop the weirdness coming through, helped by her new friend and mentor, Tankerton Slopes.

In the first series finale, we discover the existence of many other parallel Londons, such as Donlon, a more boring version, or LONDON!, where everyone is an angry cockney. We also meet Edna's half-sister, Ida, and their father, The Prince.

Tropes used in Undone include:

A Day in the Limelight In series 2, we get an episode from (London) Carlo's bewildered point of view
Alternate Universe Or, more specifically, Alternate Londons.
Britain Is Only London Oddly so for a British programme. There are many alternate versions of London, but the rest of England is rarely mentioned.
Foreshadowing Plenty of this throughout.
Idiosyncratic Episode Naming Except for the pilot, all the episode titles begin with "Un".
London Town The show is set almost entirely within London. The stereotypes exist as alternate versions.
Mineral MacGuffin The Gem, split into five Gemlets, a key part of series 2.
The London Underground Heavily features in the third series episode "Underground", surprisingly. Also, the first episode's title, "Mind the Gaps" comes from the Underground announcement.
Unreliable Narrator Mentioned as a possibility in the third series finale.
Unseen Audience Series 3 finale. Edna has been telling this story to all the other characters, as a part of the Cancellation Point.