(1) In this section, "the relevant period" means -
(a) where the amount chargeable arose under section 98, the period treated in computing that amount as being the duration of the lease;
(b) where the amount chargeable arose under section 99, the period treated in computing that amount as being the duration of the lease remaining at the date of the assignment;
(c) where the amount chargeable arose under section 100, the period beginning with the sale and ending on the date fixed under the terms of the sale as the date of the reconveyance or grant, or, if that date is not so fixed, ending with the earliest date at which the reconveyance or grant could take place in accordance with the terms of the sale.
(2) Where in relation to any premises an amount (in this section referred to as "the amount chargeable") -
(a) has become chargeable to tax under subsection (1), (2), (3), (4) or (5) of section 98 or under section 99 or 100, or
(b) would have become so chargeable but for section 103(3) o
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