In which The Proclaimers have 487 miles on me.

I've just signed up to walk half a marathon with my friend Liz. For those of you familiar, it's The Moonwalk - not a mass exercise in walking backwards like Michael Jackson, before my father can make the joke, but a nighttime hike through London, wearing nattily decorated bras, to raise money for breast cancer.

I've wanted to do it for years - in equal parts to raise money for breast cancer and because lots of people I like to stalk on Twitter do it. But until I signed up, handed over my registration fee and thought up a hilarious team name (The Worthing Domes, if you'd like to reward us with a few rofls), I hadn't given much thought to the walking-13-miles part of the deal.

I know you're all terribly fit and virtuous people who jog to Eastbourne and back before breakfast, and so to you this won't seem much of a chore, but I'm apprehensive. Actually, my legs, feet and cardiovascular system are apprehensive. My head, meanwhile, is going "Pff, it's walking! How hard can walking possibly be?" while ordering a second slice of pie.

In theory, I can do walking pretty well. I can do it in heels, while holding several full Sainsbury's bags, texting and reading a book, and 85 per cent of the time still not walk into a lamp post. During my short but enthusiastic time as a gym-goer, walking on a treadmill was certainly the thing I was best at. Had walking been a PE subject at Davison, I might have been Games Captain*.

 But since I've had sufficient income to buy a weekly travelcard, walking has become a skill I don't use as standard, but regard as something impressive to be saved for special occasions  - like a Boxing Day stroll down the seafront, where I will repeatedly take deep breaths, do power arms, and sigh "I do LOVE a good walk" to anyone in earshot. The trouble with living in London is (and I'm sorry to anyone reading this in drizzle at a bus stop, having waited 40 minutes for a Stagecoach to High Salvington), we have a lot of transport. Loads. It's not always reliable, of course, but still there's scarcely a journey I make that doesn't have the option of a nice dry bus or tube to save me using my joints for half an hour.

And as having a travelcard means that I've basically prepaid for ALL OF THE TRANSPORT in zones 1-3 for a month, it simply seems bad economy not to entrust my backside to TFL whenever possible. From Euston station, for example, there are two buses that can carry me one stop to the door of my office. It's a distance I could practically forward-roll if required, but still - the buses are there. Right there, calling to me. If anyone from work might see me, I naturally keep on walking out of shame; but if the coast is clear, I'm on that bus quicker than you can s - oop too slow, I've arrived!

So, you understand extent of my challenge. I won't be able to get a bus during the Moonwalk. Or a skateboard, or a piggy back - I know, I've checked the rules. It'll just be me, Liz and my bunions, for 13 miles. My best plan of action, I think, is to try to make it feel as much like Boxing Day as possible, so I'll eat an enormous turkey stuffing sandwich beforehand and sing Slade on the way.

*Provided all conventional sports on the syllabus were removed and replaced with 'sitty downy badminton', at-desk disco dancing and  high-impact backcombing.