I thought some of the posters on the NS thread might enjoy this. Its from 1976 - a 30 min interview. If you Google her name and Desert Island Discs it comes up straight away.
I enjoyed it, she seems an interesting mixture of rebellious (for her time) and rather Establishment.
There are quite a lot of other interviews with children's authors on DIDs, if anyone is interested - Rumer Godden, Shirley Hughes, Jessica Mitford (I know she wasn't a children's author but I loved her books as a teenager).