The photographer will always be the first owner of the copyright in the pictures he takes, unless he is employed to take them as part of his job, in which case his employer becomes the first owner (think of a staff photographer for a local or national newspaper). Someone who commissions a freelance photographer to take pictures, or merely permits the photographs to be taken at an event, would have no claim to the copyright unless it was stipulated in writing beforehand as part of the commissioning or other agreement. In my experience photographers rarely relinquish their copyright if there is a chance they can economically benefit from some further exploitation of their work beyond the original purpose. Instead they license interested parties to use the images for specific purposes or territories or durations, or a mixture of all three (see the fourth question on this page
for more details).
My guess would be that in circumstances such as those you describe, the photographer will indeed be the copyright owner, although it is possible that he issued the event organisers a licence to use the image(s), perhaps for publicity at future events. If that is so then it will depend on the terms of the licence whether the photographer has allowed the organisers to issue sub-licences, meaning that they could authorise you to use the pictures, without reference to the photographer. The photographer should be able too clarify the situation.
It is worth saying that if you haven't actually published your book, you are probably not liable for infringement, because at this stage what you have done would probably fall within the exception for research and private study (section 29
of the Copyright Designs and Patents Act). Were you to have gone on to the next stage and published, it would probably be secondary infringement (dealing in copyright works in the course of business) and because you were relying on the authorisation from the event organisers, you would have a defence of honestly believing that the photograph was not an infringing copy (see section 23
). However a clever lawyer could easily argue that publishing, even though the image had already been published elsewhere, would amount to primary infringement (contrary to section 18
In any case, assuming you still wish to use the disputed image(s), there is no point in antagonising the photographer if you need to negotiate a licence with him.