Fortunately, I was lucky. You get sent a magazine telling you if you've got in or not. My flatmate wasn't so lucky — there's always next year Andrew!
If you don't get a place in the ballot then you can always try and get one through a charity like Cancer Research UK or the WWF. You usually have to raise between £1,000 and £2,000.
It's possible to train for a marathon in around 17 weeks if you have a relatively good level of general fitness to begin with.
You should start by getting yourself a shiny new pair of running shoes. Get your stride analysed by an expert who can recommend pair of trainers that will offer your feet (and joints) the support they need.
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If you want to look like a pro, stock up on other running gear while you're at it.
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Oh, and make sure you have a good set of headphones. The Bose SoundLink headphones I used doubled up as ear warmers during the cold winter training months.
You will have to sacrifice your weekends for ridiculously long runs, some of them up to four or five hours, depending on your pace.
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You are advised to run one or two half marathon races before-hand. I did one in Cambridge in the middle of February and it was freezing.
The Royal Parks Half Marathon in London is another good half marathon.
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When you train for a marathon, you get to know pretty much all the roads (and parks) in your area.
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You also get to see some pretty good sunsets on those evening runs home from the office. Beats taking the Tube.
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But running isn't always so pleasant. You'll soon start to despise all the tourists that get in your way around popular London landmarks like the Houses of Parliament.
You can use running as an excuse to explore other cities while you travel.
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The furthest run you need to do before the actual marathon is supposed to be around 20-22 miles. Anything more than this and you risk injuring yourself before the big day. I found running on treadmills harder than running outside.
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