7. An alteration to a school to provide that–
(a)a school which was an establishment which admitted pupils of one sex only becomes an establishment which admits pupils of both sexes; or
(b)a school which was an establishment which admitted pupils of both sexes becomes an establishment which admits pupils of one sex only.
For the purposes of this paragraph a school is to be treated as an establishment which admits pupils of one sex only if the admission of pupils of the other sex–
(a)is limited to pupils over compulsory age; and
(b)does not exceed 25% of the number of pupils in the age group in question normally at the school.