Import duty and tax is hit or miss, really. I've imported lots of items from the US and other non-EU countries, sometimes it arrives on the doorstep, other times you get the dreaded Duty Payable card instead.
It appears to be dependent on the carrier, if ParcelForce are involved - you're gonna pay duty and VAT!
I imported a Sightron SIII and got nabbed for duty and VAT, it still cost less than £400. I think I paid around £380 in total, but the exchange rate is also a factor.
With every day that passes I'm forced to add another name to the list of people that have pi$$ed me off!