In the US NIS $29.99 in the UK £51.44. Why

Checking the price for Norton for my mobile I made the mistake of going to the US site and saw the price in USD. On changing to the UK site I found that the price was the same but in GBP. As shown in the subject line this is a vast increase on the US price. Yet again we seem to be paying a vastly inflated price for something just because we are on the other side of the Atlantic. Might  I ask , WHY?