18.—(1) Subject to regulations 16 and 17, a local authority may, in determining budget shares, take into account in their formula, as they consider appropriate, any or all of the factors or criteria set out in Schedule 3, as provided for in that Schedule.
(2) A local authority must, in determining budget shares for both primary and secondary schools which they maintain, take into account in their formula a factor or factors based on the incidence of social deprivation among pupils registered at all such schools.
(3) A factor included in an authority’s formula pursuant to paragraph 19 of Schedule 3, is not, for the purpose of paragraph (2), a factor based on the incidence of social deprivation among pupils registered at a school.
(4) The factors and criteria set out in Schedule 3, may not be taken into account by a local authority on the basis of actual or estimated cost unless otherwise stated in that Schedule.
(5) Where a local authority take new factors or criteria into account in their formula or delete factors from their formula or determine a formula substantially or wholly different from the previous funding period, they may make such transitional provision as they consider reasonable.