Thanks for all the responses. I suspect they didn't realise the bag they nicked had my logbook in it. They removed other things from it beforehand. In hindsight, they were quite considerate and it could have been a lot worse.
I have a new logbook now, and Mrs bcfc will start transcribing shortly...well, she's the only one in the house with legible handwriting.
This time, it will be kept in the safe and only taken out when needed.
Just a thought, if my license had also been stolen, would I be grounded until I had a replacement or is it not to do with the physical possession of the documents?