“original school, college, university or hospital building” means any original building which is a school, college, university or hospital building, as the case may be, other than any building erected at any time under Class M; and

“school” does not include a building which changed use by virtue of Class S of Part 3 of this Schedule (changes of use) F1or which was erected by virtue of Class CA of Part 4 of this Schedule (temporary buildings and uses),