21.—(1) Except as provided for in this regulation, in determining and redetermining budget shares for primary and secondary schools maintained by it, a local authority must ensure that an amount equal to the guaranteed funding level is included, calculated in accordance with Schedule 4.
(2) For the purpose of determining budget shares, paragraph (1) does not apply to any school opening during the funding period, except in the circumstances set out in paragraph 3 of Schedule 4.
(3) This regulation does not apply in relation to a redetermination of a budget share under regulation 11(5) or (6).
(4) A local authority may change the operation of this regulation and the operation of Schedule 4 in determining and redetermining budget shares where authorised to do so by the Secretary of State under regulation 29 (alternative arrangements).