Taken from HMRC website:
"Are there any reliefs from Duty and VAT?
Yes, they include:
Goods of £18 or less in value (excluding postage, packing and other miscellaneous costs) this does not include alcohol, tobacco products, perfume or toilet waters.
Gifts from one private individual to another providing the value does not exceed £36. (Exception: There is a very restricted gift allowance on excise goods but you are advised to contact Customs for further information.)
Personal effects of people returning to the EU after residing abroad.
Goods found to be defective or damaged or not otherwise as ordered. (Customs must be notified before qualifying goods can be returned overseas. Otherwise duty relief may be lost.)
Goods imported into the EU for processing and repair before re-export from the EU. (Your local office of HM Customs and Excise can provide you with further details.)"
My invoice from Amazon breaks down as follows:
Subtotal of Items: GBP 23.26
Shipping & Handling: GBP 4.30
Promotion Applied: -GBP 0.00
Lightning Deal: -GBP 6.64
Totalling £20.92, including shipping. So minus the £4.30 shipping and handling fee and it comes to £16.62. If they try to charge any import fees, I will argue the toss as Amazon clearly state the item price as being less than £18 before shipping.