(1) In this section "taxable period" means a period in respect of which a person is required, by any provision of excise law, to make a return of the excise duty payable by that person for that period and to pay that amount.

(2) Subject to subsection (4), an assessment under section 99A or an estimation under section 99AA may be made at any time not later than 4 years from -

(a) except where paragraph (b) applies, the date of the transaction giving rise to the liability concerned,

(b) where the liability is in respect of a taxable period, the last day of such period.

(3) Subject to subsection (4), proceedings for the recovery of an amount of excise duty may not be instituted, or other action for such recovery taken, unless a notice of assessment, or another notification in writing stating that such amount is due, has been issued by the Commissioners before the expiry of a period of 4 years from -

(a) except where paragraph (b) applies, the date of the transaction giving rise to the liability to that amount,

(b) where the liability is in respect of a taxable period, the last day of such period.

(4)