The notice must state whether the current or previous accounting reference period—
is to be shortened, so as to come to an end on the first occasion on which the new accounting reference date falls or fell after the beginning of the period, or
is to be extended, so as to come to an end on the second occasion on which that date falls or fell after the beginning of the period.
A notice under this section may not be given in respect of a previous accounting reference period if the period for filing accounts and reports for the financial year determined by reference to that accounting reference period has already expired.
In this section "UK undertaking" means an undertaking established under the law of any part of the United Kingdom ....