This compares to annual per prisoner private prisons operating costs as follows: o For Addiewell, a cost of £36,034, being £4,385 more than the average cost; and o For Kilmarnock a cost of £24,010, being £7,286 less than the average cost. - There are public prisons operating at both higher and lower cost than the private prisons. - SPS has identified comparator prisons, being Low Moss prison for Addiewell and Perth prison for Kilmarnock: o Addiewell has an annual cost per prisoner of £36,034, which compares to the equivalent cost for Low Moss of £24,363 (i.e.