If you use dutycalculator.com it will tell you what VAT and duty you'll end up paying precisely and will work out a "landed cost" so you can work out if it's cheaper to import
the annoying bit is that is the duty is over £50 the the courier companies often aren't willing to cover it upfront and you have to put up with a delay while they contact you (often by post) requesting this payment. Fortunately last thing i imported was just under £50 but had this in the past