Unfortunately I think you are right. There aren't any.
With one new exception, although may be too far from you in S Wales. Arc of Attrition by the Mud Crew. 100 miles round the end of Cornwall in early February! Doing that should satisfy the running long bug for a few weeks!
The event in 2015 will be the first time this 42 miler will be run. It takes over from the 50miler but that was organised by Ultra Race. The 2015 run will be organised by RunWalkCrawl. They are a new team. I did their Gower Ultra recently and they did a great job, so this is on my "to do" list for 2015.
I am going by train from Wiltshire to Waterloo to Euston then out to Tring. The only problem I always have is that I cannot get there for the 11am start. End up at the back of the fast guys leaving at noon, then finishing day 1 in the dark. A pity, but the only way if I do not stay overnight closer.
This was a brilliant event. The beach running was superb, the coast path views stunning. The organising team made everyone feel really welcome. This should become a classic ultra challenge. It probably will not as it is too far from London, which is just as well as I also enjoyed the low key atmosphere.
Yesterday's weather certainly helped, even the marshes looked great in the late afternoon sun. This is definitely a race to do in 2015.