Right...
If there is no stated "Specific Item Code" on the parcel, identifying its contents and therefore the amount of Duty payable (3.2% for markers 2.7% for bolt on's), it will be charged at the flat rate, which is 7%.
If the parcel is marked as $500 value...plus say $40 for shipping, you will pay duty on $540.
$540 is roughly £307...
Duty and VAT will total 24.5%...£75.22
Also...the UK shipping agent, being Parcel force or whoever, will also add a collection fee...£13 give or take a bit
So..your Nightcast cocker, will cost you around £395 and 22 pence.