In reply to Michael Hood:
It was priced at £5, I paid quite a bit more which surprised the woman behind the counter who couldn't believe the book was at all valuable. Maybe the same shop where I found a long out of print and valuable book on botanical illustration, again I paid well over the asking price.
Both several years ago, I think Oxfam now check on line prices if they have any suspicion that a book is valuable although that does rely on the volunteers being aware that something, possibly very specialised, is potentially worth more than the majority of novels etc that end up in Oxfam