Sorry, I wasn't clear - in this case the value of the goods, converted from dollars to pounds, came to just over the 40 sterling. As I said, I had an extremely generous Santa. And then, because the package was sent express delivery, another rule kicked in which meant they could take into account the cost of shipping.
In any case, it's a major kick in the teeth for all sides, and I can't understand how the cost of express delivery (already incredibly expensive) wouldn't automatically include other charges if they know this is the regulation. Which of course they must do - unlike those of us who send very few international packages.