How many places do charities get at the VLM? After a quick search online, I haven't found any relevant data. This is a key question because it might be perception rather than fact when it comes to the number of charity places.
Those saying that only those runners who can achieve a GFA time can really call themselves committed should consider that the VLM GFA for men aged 18-40 is 3:05. Only 1946 male runners achieved that at any marathon in 2013, including quick marathons like Berlin and Abingdon.
I ran the South Downs a couple of years ago. It's challenging and also beautiful. Salomon also sponsors the Kielder Marathon, which calls itself 'Britain's most beautiful marathon' and I believe is slightly less challenging than the South Downs. I'm considering running it this year.
I've run three marathons now. I used energy gels in training and running the first two. For the third one, I didn't take on anything during training or the marathon itself except plenty of water. I performed better in it than the others. I ate an enormous amount of food in the 2-3 days before the race, especially in the 24 hours preceding it.
Anita Bean in The Complete Guide to Sports Nutrition (my food bible) has useful tips on 'carbo-loading'. Essentially go for 7-8g of carbohydrate per kg of body weight for 3 days then 8-10g/kg for the next 3 days before the race. Eat a substantial breakfast 2-4 hours before the race.
Feelings of hunger are often caused by lack of water - this is true whether or not you're exercising - and feeling hungry after 15 miles is probably an early sign of impending dehydration rather than a lack of fuel.