Also of interest might be this search page which gives 20+ pages of radio and TV.
But it isn't sortable & doesn't indicate which pages have available programmes.   
It's useful to see what the BBC has broadcast in the past though.
www.bbc.co.uk/search?q=Folk

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other BBC collection pages

Category : World - radio
Current shows; a wide interpretation of 'world' plus a few extra programmes.
- open in a browser -
www.bbc.co.uk/sounds/category/music-world

Genre : music : World - radio & TV
www.bbc.co.uk/programmes/genres/music/world/player