As above there will be no duty just VAT and customs charges (applied by Royal Mail/courier).
Something worth being aware of is that customs have tightened up on the rule about the cost of postage/shipping being included in the vatable value of the goods so if it cost you £16 but shipping was £10 then the value for customs purposes is £26. This can mean being charged a fair bit more potentially. Some couriers are very strict on applying this rule and others less so.
That’s not what is says here Intrinsic value
1.What does HM Revenue & Customs (HMRC) mean when they refer to the import of low value goods?
Imports of low value goods are any consignments, made up of goods of a negligible value, that are dispatched direct from a third country (non-EU) country to a consignee in the EU which may be admitted free of customs import duty and/or import VAT.
Currently this means that:
consignments with an intrinsic value of £15 or less are free from both customs duty and import VAT
import VAT is payable when the intrinsic value of the goods is over £15
customs duty (and import VAT) is payable when the intrinsic value of the imported goods is over £135
2.What is the intrinsic value?
The intrinsic value is the price paid or payable for the goods excluding postage and packing and insurance costs.
Just like you I have ended up paying VAT on a couple of small items that just triggered the charges – If you go over the threshold VAT is charged on the combined cost of the goods plus the postage.