Because of two contradictory answers, I had a look. If it's an Amazon error then they'll refund the postage otherwise they'll deduct the postage from the amount that they owe you.
Considered getting in on the jewellery, but not going to take the risk. It'll probably be horrible, given the price, and don't want to take another hit on returning it under DSR.
"How do I return an item delivered by Amazon.co.uk?
Visit our Online Returns Centre to get a mailing label to return your item. We'll pay the cost of return delivery if your return is due to an Amazon.co.uk error. Otherwise, we'll deduct the cost of return delivery from the amount of your refund."
I only ask as some people pay for the returns, and hoped Amazon would be one of these.