One of the few collections of academic essays on the subject at hand, British Radio Drama is an essential book for the extended radio drama library. It's not the whole story, it's not definitive, and it's not up to date. But it covers some important topics that receive little attention elsewhere.
John Drakakis, the editor, wrote a good history of the medium in his introduction. There are essays on Henry Reed, Louis MacNeice, Giles Cooper, Dylan Thomas, Susan Hill, Dorothy L. Sayers, and Samuel Beckett. The last chapter, entitled “British radio drama since 1960” mentions Rhys Adrian, R.C. Scriven, Don Haworth, and a few others.
Perhaps the most useful aspect of the book are the appendices. Included is a list of plays with broadcast dates for the authors discussed, a list of published radio plays (very useful for scouring the internet in search of out of print copies), a selected bibliography, and extensive footnotes that lead to other sources.
The one great failing of the book (aside from being woefully out of date, since it was published in 1981) is that it doesn't connect the dots in terms of media theory. There isn't a build-up to a consensus about the medium in terms of what it essentially is. Which is why I often argue that Guralnick's Sight Unseen is so important. It's the logical next step in putting together the whole surveyed landscape of the medium in terms of why and how it works artistically.
I have found this book very useful for making additions to the Audio Drama Wiki, particularly in regards to Louis MacNeice. I will eventually tackle Under Milk Wood as well. It also has lead me to some interesting and overlooked avenues. One of the essays mentioned Muriel Spark, who apparently wrote a few radio plays herself:
Researching her and other novelists (such as Sayers, Susan Hill, and William Trevor) causes some very frustrating problems. People in the world of radio drama fandom are not always careful to distinguish between a play written by an author, and a play written by someone else as an adaptation. In the Audio Drama Wiki, we've designated these “dramatizations”, although in conversation I've often used “adaptation” and “dramatization” interchangeably. A topic for more discussion, surely. In the case I'm refering to, Muriel Spark had written original radio plays at some point, but the published versions of these does not contain broadcast information or cast information. A bit of a dead end there in terms of research for the wiki.
I also picked up this book of radio plays by Susan Hill:
They seem very interesting.
Another interesting find is in the mail. It's a book of radio plays by the blind and deaf poet R.C. Scriven. He might be my next project to tackle with the wiki. I'm hoping that the volume I've purchased contains information about him, because there is precious little to find on the internet.
And yet again, as with most of these writers, their work is unreachable in its native format. Although there may be recordings of these plays out there, many are missing and lost. And many more are poorly cataloged by collectors, particularly on the internet, who often neglect to distinguish between an original version (the one first broadcast) and later remakes. The Dark Tower, the Beckett plays, and the Pinter plays often suffer from this confusing state.