I'm not pointing a finger Simon! ................and there is no "underwater photographer's master guide to entering competitions, and also sharing and marketing images" book in existance, well that I know of anyway!
No, there is no book in existence I'm afraid - but a service explaining the hows and whys of photographic business was offered, & declined.
Photographic competitions generally ask for the right to display images to congratulate the winners and promote future contests. If there were no terms shown, then it wouldn't be unreasonable for them to do so - after all, how would anyone know what image had won if the organisers didn't have the right? If there are no terms stated, perhaps it might be better to submit the image and include the following in the rights metadata field:-
"All rights reserved. Restricted rights for XXXXXXXX (name & date) competition; image may only be used for the purposes of congratulating XXXXXXXX (winner/highly commended/ranked), and for the purposes of promoting future XXXXXXXX (name of said comp) competitions for a period of 2 years, commencing YYYYYY (Date of announcement). All other uses must be confirmed in writing with the copyright holder prior to use. Embedded metadata and copyright notice(s) must be maintained. The Artist hereby asserts his moral right to be identifed as the author of this work in accordance with section 78 of the Copyright, Designs and Patents Act 1988."
That way, everyone knows what use they are getting.