Phil, a very interesting link to the article in The Scotsman. Where even Dr Ardrey states -

"I am hoping the book provokes debate and discussion,” said Ardrey. “But if I’m right, then 100 years of British history needs to be rewritten"

Therefore I can only surmise, that he himself has doubts about his conclusion. Therefore the mystery is still just that, a mystery and everyone who makes a living from it will be the better for it.