You're allowed to receive occasional
bona fide gifts, from outside of the EU, without paying any charges as long as the the value does not exceed �36. Those gifts must be sent from one private individual to another. Anything ordered from, or sent by, a store does not qualify.
Other than the 'gift' allowance, the rules are complicated but it basically comes down to saying that if you import anything worth more than �22 (currently �17.43) you have to pay charges, otherwise you don't.
If your shipment doesn't meet the 'gift' criterion or if it's worth more than �22 (or even if it does fall into one of these categories but it doesn't carry a correctly filled out CN22 customs form), you'll have to pay import tax and/or VAT, plus an �8 customs inspection fee.
The way that the charges are worked out is explained in my post here:
http://www.theanswerbank.co.uk/Law/Civil/Quest ion623598.html
Chris