Here is an article by BTB where she says that she found out her mother was illegitimate in 2004:
http://www.telegraph.co.uk/culture/t...workhouse.html
I can't find the ones that I read but I know that in one of them, she said that many years ago, when she was promoting one of her bestselling books she went on a book tour to Australia and because she knew that some of her mother's siblings had emigrated to Australia, she made a big thing of it in her interviews over there in the hope that they, or their children, would get in touch with her, and because she didn't hear from anyone, she took it that they weren't interested. But it does seem that she didn't know how they came to emigrate until the making of this tv series.