In reply to:

Most of the evidence comes via Joseph Sickert, Walter's son, and relies on hearsay, and "remembering" what his father had told him.

I thought that Sickert was childless and that Joseph "Sickert" was a fraud. Anyway, I was just wondering if anyone else had read the book. It is very interesting. I think it is a shame though that she destroyed one or more of his paintings.