(1) Tax chargeable under section 3(a) or (c) shall be due -

(a) in case an invoice is required under Chapter 2 to be issued, at the time of issue of the invoice or, if the invoice is not issued in due time, upon the expiration of the period within which the invoice should have been issued,

(b) in case a person is liable under section 69(1) or (2) to pay an amount of tax by reference to an invoice, or credit note, issued by him or her, at the time of issue of that invoice or credit note,

(c) in the case of continuous supplies of telecommunications services or electricity, or of gas which has the meaning assigned to it in paragraph 17(3) of Schedule 3 -

(i) supplied to a person other than a person to whom an invoice is required to be issued under Chapter 2, and

(ii) for which there is a statement of account (being a balancing statement or demand for payment which issues at least once every 3 months),

at the time of issue of the statement of account in respect of those supplies,