5.—(1) Subject to sub-paragraph (3), where a person on whom a financial penalty has been imposed fails to pay in full the financial penalty or any instalment thereof by the date on which its payment is due, that person shall be liable to pay to the Commission interest, calculated on a monthly basis, on the outstanding amount of the financial penalty or instalment (as the case may be), at the rate of 6% for so long as such outstanding amount of the financial penalty or instalment remains unpaid.
(2) For the purposes of sub-paragraph (1), any part of a month during which any outstanding amount of a financial penalty or an instalment thereof remains unpaid shall be treated as a full month.
(3) In respect of any financial penalty that was imposed before 19th April 2010, interest shall be payable in accordance with sub-paragraph (1) only as from that date on the amount of the financial penalty or any instalment thereof that is outstanding on or after that date.