Interest on excess tax refund may be charged when refund exceeds assessment amount, triggering monthly interest liability. Where a refund granted under the initial assessment process is not due on regular assessment or exceeds the refundable amount on regular assessment, the assessee must pay simple interest on the whole or excess refunded for the period from grant of refund to the date of regular assessment at the statutory monthly rate. If a subsequent order holds the refund to have been correctly allowed, any interest chargeable shall be reduced accordingly. An assessment made for the first time under re-opening or special assessment procedures is treated as a regular assessment, and the provision may apply to earlier assessment years where proceedings finish after the effective date.