Ripping yarn set in the 40s in a school rather like Verdala. In fact a Verdala with public school boarders. Think of Biggles, Famous Five, Jennings and Boys' Own all rolled together and set in Malta.
Who was Peter Jackson? He must have known Verdala (it wasn't Peter Prictoe, I asked him).
A search on www.bookfinder.com reveals plenty of copies available. (Thanks to Chris Barber for that info). Also on ebay from time to time. Much cheaper without a dustjacket.