I read teh other day that teh tax rules changed in the summer but no one wanted to shout about it. Probably not relevant as it’s a frame but I think it was something like you now only pay import duty, not VAT, on items less than £108 (or some random value like that).
Otherwise it’s VAT @ 15% + import duty @ ? . Unless it’s second hand then I don’t think you pay VAT.
USA or Canada should be the same as it is Uk that makes the charges.
I think you should be able to get the vendor to take off any local taxes as it is being exported, in the same way tourists over here can reclaim VAT paid on more expensive items.
That’s my understanding, I’m sure I’ll be corrected soon by someone more knowledgeable if I’m wrong 🙂