The 'import' VAT rate is the same as whatever it is normally - 20% for most things.
Duty and VAT are charged on the total (declared) cost of goods plus postage. This is because in the past some unscrupulous traders would sell something for £0.01 and then charge £10/50/500 for the postage. Loophole closed!
Duty is calculated first (if applicable) and then VAT is charged on the total of goods, postage and Duty (Yes they charge VAT on the first tax !@!.
The importing carrier - PO/Parcelfarce, Fedex, UPS, whoever, is required to collect the relevant charges for HMRC. The 'clearance fee' is their charge for providing this service. It is decided by each carrier but is not dependent on the value of the transactions. £8 is very cheap - I've seen £20.
As Sandy says, this is as it has been for many years now. It's taxes - it'll help pay for flood defences, or the NHS, or MPs expenses ...