it's one of those 'you either know it or you don't'
A peter is another word for a safe. A peterman in the good ole days when people used cash, was the safecracker or safeblower on a naughty little earner.
Thank you. I've heard of a peterman but for some unknown reason thought the peter referred to the explosive used to crack the safe... You learn such a lot from crosswords (or from people who solve them!)
Jazzgirl, thank you I used your link and was amazed at the heat generated by one fairly unimportant clue! Fascinating, and I'm still not convinced who has got the truth of it...