Sole trader - bike as a tax write-off?!?

I spoke to a book-keeper about this a couple years ago and her opinion was that I could claim a percentage of the bike's value. Just an opinion though, she wasn't a full accountant and had never looked into bike specifics in terms of tax before.

If anyone has a definitive answer it would be useful for plenty of forumongers I expect.

I'm not too sure on the bike purchase thing, but my accountant asks for my mileage as you can claim a certain amount per mile. I must ask about the purchase of a new bike though.