Thanks Simgull and Dazzer for the feedback/advice. Being my first organised running event of any sort I'm naturally starting 2 feel a little nervous and the weather being as it's forecast was not something I had anticipated!
There should be enough of a coolish sea breeze to keep body temperature down. You should be fine. Run with a soft hat to keep sun of head and to draw moisture. Beware of getting sun cream dripping into your eyes as you sweat.
Good luck!