Technically, and officially, you will get charged the VAT on your "import" regardless of it being new, second hand, a gift etc.
Some items also incur an additional customs charge, and will depend upon what it is (most obvious example is tobacco).
You will also be hit by an "administrative" charge by the UK handling company (courier) which can vary from £10 to £30+
You might also get lucky and avoid all these charges
A good customs declaration can help avoid, or reduce these charges, but if the parcel goes missing, insurance will be based upon the declaration!
I occasional buy electronic equipment from USA, but is has to be unavailable in the UK to make it worth the hassle.
Peter