I guess you are talking about HM Customs in the UK, customs used to have big black books with all the tarriffs, the problem always was classifying the goods, and you have VAT as well, also depending on the value you may have to pay broker charges for clearance, but somewhere along the line you should have a detailed invoice.
Here's a link that might help if you bought on the intenet
http://customs.hmrc.gov.uk/channelsP...yType=document
Ask a friendly clearing agent at the nearest import point