Thanks a lot for the reply! The GPS logger doesn't have any settings besides how often to record a point and if the software has one I've never changed it. The camera was set to BST (daylight savings time for the UK) which was the local time when the photos were taken and is one hour ahead of UTC.
I don't think I explained the problem very well though. I could understand it if the difference was always one hour, however, it varies:
2015/07/19 - 2 hours
2015/07/26 - 2 hours
2015/07/29 - 1 hour
2015/08/05 - 2 hours
2015/08/15 - 1 hour
2015/08/16 - 2 hours
There is a problem with the logger which I described on another forum:http://www.bleepingcomputer.com/forums/
It could be related but since the gaps aren't exactly an hour I'm guessing it's not. I've been treating all of the photos and logs the same so I don't understand why this has happened.
Any other suggestions (about this or the linked problem ha ha ha) would be greatly appreciated!