To provide a few more details, here's how taxes are calculated on ALL goods from outside of the EU:
First (where appropriate), Excise Duty is calculated. (Since Excise Duty only applies to alcohol and tobacco products, it can generally be ignored).
Then Customs Duty is calculated. Rates vary dependent upon the type of goods. For some things, such as books, its zero. For electronic items it's often between 2½% and 7½%. For cotton clothing it's 12%, except when importing from the USA, when it's 27%. (That's a penalty tariff on imports of cotton clothing from the US, because the US Government provides subsidies to US cotton farmers which breach World Trade Organisation rules).
However if the value of the goods is less than £135 then there's no Customs Duty to pay anyway. Customs Duty is also waived if the amount calculated comes to less than £9.
Then import VAT is calculated. It's charged at 20% on the cost of the goods, on the carriage charges and on the Customs Duty. (Yes, that really is a tax on a tax!).
However some goods (such as books) don't have VAT on them anyway and VAT isn't charged on any goods with a value of less than £15.
If, at that stage, there's nothing at all to pay, the Customs Examination Fee is waived. Otherwise £8 has to be added to the charges above.
Bona fide gifts, of up to £36 in value for each recipient (as it's permissible to send gifts for, say, different members of a family in a single package) are subject to the same rules as above with regard to Excise Duty and Customs Duty but VAT isn't charged on gifts valued at less than £36.
There are also different rules for perfume and toilet water.
If a package arrives without a
correctly completed CN22 Customs Declaration attached it's liable to be seized and the addressee could potentially face prosecution for seeking to evade taxes.
http://www.hmrc.gov.uk/customs/post/buying.htm