If I may, first of all, it's not currently 5% to 7%. As one of the opening sets of remarks said, it's set at the treasury bill rate, rounded up to the next point plus two. Currently the treasury bill rate is, I believe, less than 1%, so currently the interest on overpayments is 3%. It has been 5% to 7%, and it's been higher in the past, reflecting the treasury bill rate of the past.
It's set by law. Parliament enacted a law in 1989 providing this rate.