There is a one hour Canadian radio drama version of The Place of the Lion from 2003, which is available online:
This is performed live, before a festival audience, and by Canadians (i.e. not native English accents) - so allowances must be made; but its heart is in the right place; and there is plenty of humour as well as a clear and strong exposition of the profound, Platonic aspects. The combination of philosophy and jokes is very Shavian - and this broadcast was indeed done at a Shaw festival.
If you like what you hear - the abbreviated play-version may encourage you to 'read the whole thing' - and indeed might prove helpful in understanding what is going-on in some of the trickier parts of the novel.
PloL is my absolute favourite of Charles Williams's novels - which I have read multiple times over a span of thirty-plus years (indeed, I wore-out my first copy!).
It was also a vital catalyst for both CS Lewis and JRR Tolkien in the fiction writing; to the point that I don't think Lewis's Space trilogy would have been written without it, and Tolkien's Lord of the Rings might just have been a kids sequel to The Hobbit.
H/T: Thanks to David Llewellyn Dodds for pointing me at this.