[Closed] What's the official line on bringing a bike back into the country?

I'm off to the states for a few weeks and taking the opportunity to buy a bike to ride there. So I'll be bringing it back... As a bike I've bought and ridden "for personal use" can I be caught for import duty and UK tax on my return? Or because I've bought it in the states, paid their tax and used it am I in the clear? Unless it's a hard line of "anything you bring back" it seems a bit of a grey area - or is it in theory that black and white?