See here:
http://tinyurl.com/yj26e6w
Excise duty on spirits is charged at a rate of £22.64 per litre of pure alcohol. So a 0.7 litre bottle of 40% ABV booze will be charged 0.7 x 0.40 x £22.64 = £6.34
Other rates are here:
http://www.hmrc.gov.uk/budget2009/bn86.pdf
If the value of the gift exceeded £36 you'd also have to pay Import VAT at 17.5% (temporarily reduced to 15%).
Additional there's a customs examination fee to be paid. For postal imports the fee is £8 (unless certain express services are used, in which case the fee is £13.50).
Chris