Go to the website below. Click on a left-hand number that describes the watch. On the next page click on an indented number that further describes the watch. Repeat for the next page. On the final page, select USA as the country of origin and click on 'Duty Rates'.
That will show you the EU duty as a percentage. VAT will be charged on the combined value of the cost of the item plus the cost of the postage - it's how Customs calculate what it's worth.
Then it will have to be cleared from Customs and delivered to you by an agent acting on your behalf. Royal Mail will do this for around, (if I remember right), £8.50, while UPS will charge you £11.00, both collectable from you at your door.
Quite a rigmarole, innit?