Tax is one thing, and, apart from VAT, we don't usually have to pay duties on the type and value of shaving gear we import from anywhere outside the EU. On the other hand, the Royal Mail £8 is a fee or service charge for doing sweet FA. For what they actually do, £2 would be excessive.
There has long been a tradition in the UK of bodies (national and local government, service providers, rail companies - you name it) slipping in snide charges, hidden fees and taxes, and the rest. Being Brits, we generally shut up and meekly put up with it. Other citizenries, with more robust views on such things, either refuse to pay, or riot in the streets; or both.