I may be wrong and I know it will sound kind of crazy, but I believe UK Customs and Excise use declared or estimated market value when assessing duties and taxes. The fact that an item is provided free of charge does not effect the fact that an item of certain value has been brought into the country. This is because you could, in theory, be intending to sell it on and so effectively converting it back into cash. To avoid such charges you, as the recipient, must be able to prove you have had the item in your ownership for at least 6 months and that no duties or taxes were due at the time of purchase/importation.
What I have never understood is why I have to pay tax on the shipping cost as well as the product value... it's not like shipping is a tangible asset is it.
Once an items value exceeds the UK Customs threshold it becomes an asset on which Duties and Taxes may be payable.
I even got stung badly when importing five new Dell laptop plastic case assemblies from the USA.... the rules declared them duty payable as 'petrochemical based plastics' whereas as laptop spares they should be duty exempt... I had to pay the duty.
Countries Customs rules seem very variable depending upon who looks at the consignment.... sometimes you are lucky, other times not, and you get a bill.
Interestingly, I received the VAT bill for my Rigol scope a month after the unit had been delivered to me. DHL said they had paid the VAT on my behalf and now needed to recover the money. In such a case you have no opportunity to discuss any disputed value or product categorisation before the duties and taxes are paid.
I personally found the Customs office in Darwin to be a very friendly and reasonable group of people who provided me with help and advice on many occasions. They even admitted that they had failed to tax me on an occasion but were not going to bother pursuing the matter ! I don't think the UK Customs Officers are so friendly but then they are somewhat busier