In reply to Tony the Blade:
Thoroughly doable. Start with that attitude and the rest is just logistics and planning
I'm doing it in 2014.
I've run a few flat marathons, and a few hilly ultras so I'm looking forward to it. As you say you've not run a marathon before, definitely get one under your belt before then, because its tough enough the first time, but the terrain, possible bad weather and the hills will make this taxing.
You say you're near the New Forest - I did 'The Beast' once, run by Poole AC (its a half marathon around Corfe Castle and down up and along the cliffs - lives up to its name). Give it a go and you'll have an idea of what you're letting yourself in for.
Apparently there are still places next year in the MB 10k. Why not ease in with that? You'll get a recce of the area, get an idea on the logistics of the event and get some great training runs in. My first marathon was London, where I lived at the time and I was glad I didn't have to factor in travel and acclimatisation - there's enough to worry about with your first marathon.
Go for it and best of luck.