It will be on hmrc.gov.uk
It's kinda complicated though.
You can ask them,but most of the time sellers will not do it,especially on a high price item,because if it goes missing they will not get there money back for what the item is truely worth,only what they declared. Also if customs open the package and see it's a high end item,they could get in trouble.
Sometimes if customs are feeling extra mean they will still charge you.
''1) Customs Duty. - Customs duty is calculated by Customs on the "END COST" of the clothing. They add together the purchase price, + any insurance, + shipping costs. This gives the END COST figure. They then look at the material the clothes are made from. On the END COST they charge Customs duties of 12% for "fabric" clothing made from cotton, silk, nylon, polyester etc. If the clothes are leather the duty charge is 4%
2) V.A.T. - After adding the customs duty to the total cost of the clothing, they then add V.A.T.@ 17 1/2% on the after Customs duty figure. ''