If the whole or any part of a penalty is not paid by the date by which it is to be paid, the unpaid balance from time to time shall carry interest at the rate for the time being specified in section 17 of the Judgments Act 1838.
If an application is made under subsection (8) of section 57C above in relation to a penalty, the penalty need not be paid until the application has been determined.
If the appropriate authority grants an application under that subsection in relation to a penalty but any portion of the penalty is not paid by the date specified in relation to it by the appropriate authority under that subsection, so much of the penalty as has not already been paid is to be paid immediately.