23(1)Where a lease is assigned, anything that but for the assignment would be required or authorised to be done by or in relation to the assignor under or by virtue of—
(a)section 47 (contingency ceases and consideration is ascertained: duty to make return),
(b)section 51 (return or further return in consequence of later linked transaction),
(c)paragraph 3 or 5 of this Schedule (return or further return required where fixed term or indefinite term lease continues), or
(d)paragraphs 12, 13 and 14 of this Schedule (adjustment where rent ceases to be uncertain),
must, if the event giving rise to the adjustment or return occurs after the effective date of the assignment, be done instead by or in relation to the assignee.
(2)So far as necessary for giving effect to sub-paragraph (1) anything previously done by or in relation to the assignor is to be treated as if it had been done by or in relation to the assignee.
(3)This paragraph does not apply if the assignment is treated as the grant of a lease by the assignor (see paragraph 22).