I really should do more research before I enter races. I had no idea that there was over 1000 m of climbs and that there was an uphill off road section at 25 or that there were sections of broken road that almost qualify as off road.
I trained for a PB and set off looking for 3:22. By half way I was clutching to the hope of nicking a PB at 3:25.
By 15 miles the heat and constant ups and downs had got to me and a sub 3:30 was the best I could hope for.
At 20 I was clinging on for survival and thought 3:45 might be on.
The thing that got to me most was the fact that I just couldn't get into a pace I felt I could hold. The ups just kept coming and the downs wern't long enough to coast. On a couple of occasions a decent stretch of flat was spoiled by a blustery head wind.
In the end, after staggering over the grass at 25 miles, I got back in 3:41:29 - Position 120/609 M50 11/31

Thanks for your help and support.

Mike