Send it as a gift on the customs form and value $0.00 and so no tax will need paying over here, but if you call it booze on the form it may go missing in the post because postmen like a drink, so call it horse liniment or some disguise name. 
Be creative 
Ive never paid any tax 
Cheers
Don't know th UK legislation but I feel you are not well informed, no offence intended. Everything imported to a country is subject to custom duties, but, for practical reasons, small items and personal post is normally exent. I recently sent two bottles of wine to the Isle of Man. What i did was simply check the Isle of Man Post webpage and check for restrictions. There was some limit in the amount of alcoholic beverages -depending on the amount of alcohol, it is not the same to send beer than whiskey-. But, even if sent as a gift, the importer is subject to pay duties based in the value of the imported good, not in what he paid for them. As I said, I sent two litres of wine and the recipient didn't have to pay any tax, but believe me, had I sent two $500 wine bottles in an insured package, the recipient would have been obliged to pay duties.
That being said, I once was told by a US ebay seller that his package to me was returned by USPS because he send it in a beer box, so they just thought he was exporting alcohol. So you are better off checking both USPS and Royal Mail webpages.
