From HMRC website:
HMRC Website
2.3 What are the limits for customs duty and import VAT?
Commercial consignments of £18 or less are free from customs duty and import VAT. For example, goods purchased over the internet with an intrinsic value not exceeding £18, will not be charged any duty or VAT but this does not include alcohol, tobacco products, perfume or toilet waters. See paragraph 2.5, 2.6 and section 3.
If you are sent a gift with a value of £40 or less, and which complies with the rules shown in paragraph 2.4, it will be free from customs duty and import VAT, but this does not include alcohol, tobacco, perfumes and toilet waters.
Customs duty becomes payable if the value of the goods is over £135 but duty is waived if the amount of duty calculated is less than £9.
There are a number of other circumstances where relief from some or all customs charges may be available. If you think your goods may be eligible for a relief you should contact the Customs Helpline for further information.
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2.4 Gifts
Goods sent as a gift that are over £40 in value are liable to import VAT. Customs duty also becomes payable if the value of the goods is over £135 but is waived if the amount of duty calculated is less than £9.
To qualify as a gift:
the customs declaration must be completed correctly
the gift must be sent from a private person outside the EU to a private person(s) in this country
there is no commercial or trade element and the gift has not been paid for either directly or indirectly
the gift is of an occasional nature only, for example, for a birthday or anniversary.
Note: if you purchase goods from outside the EU to give as a gift to a relative or friend, whether or not addressed to that person, is treated as a ‘commercial consignment’ for which the import VAT relief threshold is £18 (paragraph 2.3 refers).