The more I think about this the more I don't understand.
The VAT has been paid, but not the duty, so if alcohol or cigarettes are imported from, say, Germany, duty would be payable in the UK
But what about other things that attract duty? I've frequently bought cameras and lenses from on the internet, when they come from the US I have to pay duty, but not when they come from Germany?
Is it just alcohol and cigarettes that are exceptions to the free movement of goods?