customs tax on guitar?

hey all, moving back to the uk in may...and as soon as we get settled(and make sure nothing huge comes up to eat our money), i will be buying a much needed new guitar. the plan is to order it from america...and have my in laws(living in america) to post it to me in the uk(take all the tags off and put gift on it of course). now, i know theres a chance that even with it being marked as a 'gift', it could still get charged duty on it. I was wondering, does anyone have any idea what the duty tax would be on a guitar thats worth about $680? also, any tips to lessen the chance of getting charged duty?
thanks
chris

Not sure about the amount if you get charged--- but to lesson the chance of being charged have them mark the the custom package as previously owned household item. When you move you can send your person items without being charged-- I would treat as a personal item 

Helena

ah thank you, fantastic help, hopefully that works