In reply to EuanM:
> I've been averaging 40-45 miles per week with about 70% of that distance the weekly long run. I know this should be higher but time and recovery time have been in short supply.
why do you think this should be higher? If your aim is to finish, you can achieve this on a relatively low mileage, if you train intelligently.
> My issue is during training the wheels start to come off at about 30 miles. Some of this is fatigue but I definitely don't eat enough on route.
Eat more?
> I reckon I can push this distance out a bit by walking inclines and taking walking rests on route.
> I guess I'm asking on the longer races do (did) you find yourself walking a lot?
Yes, the longer the race, the more I walk, especially on the uphills.
> As I said, I'm only looking to finish the course and not concerned with trying to achieve a fast time. Just wondering what others experienced as the distance increased.
On very long runs the wheels will eventually come of. This can be delayed by proper pacing, nutrition and hydration, but essentially in every long ultra there will be bad patches and the ability to just tough it our is what gets your through.
Proper physical training is a base obviously, but proper mental preparedness will make difference. Once the wheels come of, but the so called "second wind" can come and feel great.