I've had various items of technical equipment sent over from the U.S. for years, and have come to the conclusion that the whole customs and import duty system is a complete racket.
There are different import duty rates depending upon the type of goods. VAT on most items is, as has been stated, 17.5% but there is a catch. Customs & Excise don't just add the VAT to the original item price. They add the import duty first, then add the VAT to the total, so you are charged VAT on the import tax!
It gets even worse though. The value that they use can be based on the declared item price
plus the shipping charges. So you can be charged import duty and VAT on
postage. The whole system is grossly unfair in my opinion, but that's the way it works.
You also need to watch the calculations very carefully. Some years ago I had a whole batch of parcels arrive with the usual red "CUSTOMS - CHARGE" stickers on them, and somebody had taken the U.S. dollar prices and calculated the charges as though the figures were pounds Sterling.