This was first broadcast in January 2014, on Radio 4 I think, and is now being repeated on Radio 4 Extra:
“The Welsh M1”, about the A470, the road connecting North and South Wales, in two episodes, with Cerys Matthews. It’s in English, but she does interview at least one Welsh speaker, I seem to remember.
Looks like it’s going to be on iPlayer for a good long time, unlike most BBC radio programmes.
