If you get charged import duty into the UK it's added to the item values & also the postage costs, first VAT and then the duty, it's cumulative. VAT is 15% Import duty around 3% it can vary but cameras etc fall into that bracket.
A rough rule of thumb is expect 20% for total import duties, however I've only paid duty twice on smaller packages out of about 40-50, so you may be lucky. That included 3 Speed/Crown Graphics, many lenses and 3 or 4 other cameras, all from the US.
Before VAT was reduced the most I ever paid was around 21%. in total on two 10x8 cameras. Some new items may be at the higher 6% rate on top of VAT
Ian