Import duty and VAT can be charged on good imported to the UK from outside the EU, over a value of about £18.
It is not guaranteed that Customs & Excise will catch you (the buyer, I mean) and enforce the payment, but unless you are willing to have expensive stuff marked as of low value (which will invalidate insurance and anyway be treated as fraud), it is always a possibility.
So it can be a bit of a lottery buying from outside the EU for us over here in the UK ... and as the fees could potentially add approximately 30%, reduce a bargain to about the same price as buying it within the EU or UK in the first place.
There's always plenty of people to say "Oh I've done it loads of times and I've never had a problem", but that's the luck of the draw ...
