That's the way it's treated in UK law, but apparently in the US, you're liable for the tax as soon as you have access to the asset. I think the same thing causes people problems with stock options. Seems like an odd bit of legislation.
Hmm, are you sure? I thought that if you held bitcoin for over a year, it would be taxed as capital gains? Meaning you don't realize the value until you sell it?
It seems to me that forks are treated more like RSUs (restricted stock units) than stock options. When a company grants you RSUs, you're immediately responsible for tax on the value of the shares. If you then hold the stock for any period of time, and later sell at a profit, you'll need to pay tax on that profit too. You get taxed twice.