Marathon Training

[Red Shell]

I've entered the London marathon next year and have somehow managed to end up with about $4000 in bets which require me to run it in less the 4 hours, all of which go to the charity i'm running for.

I'm looking for somesort of workout program to make this possible. I'm 26, 14 stone and do a 20 minute run once a week at 13km an hour.

I have plenty of time to train, (i trade the equity markets) but my program has to be flexible to allow for a few days of non training due to market movement. Theres a treadmill at work, which is what i'll be using during the week.

My workout plan is based on a three run program.

1 - 5k, as quick as i can, hopefully building up to 14/15km an hour.

2 - 15k, looking to get through it, running at around 10km an hour.

3 - 10k, looking to run at the around 13km an hour.

Hopefully by christmas i'd have worked up to this and be looking to progress up to running 30k weeks for a month or two before the main event.

How does this sound, anything you'd change, would it be better to have a more rigid five month plan?