Bright Horizons Family Solutions Ltd v Secretary of State for Communities and Local Government 
[2019] EWHC 14 (Admin)

The meaning of the GDPO fell to the courts not the inspector:

para 6:
” The role of the court in these proceedings is not in principle one of deference to the Inspector’s planning judgment. The meaning of the legislation, including the GPDO, is a matter of law, even if, as in this case, the interpretation involves determining the meaning of an ordinary word in the context of the legislation in question. The Inspector errs in law if he applies the legislation in any sense other than its true construction. My task is therefore to ascertain what that is. “

The interpretation of Class M of part 7 was complicated partially due to other changes in the GDPO

para 11:
“The primary effect of these provisions, ignoring for the moment the requirements relating to size or position of the development, is as follows. If the extension is to a school, it is within Class M. If the extension is to premises which have changed use to a nursery under Class T, it is within Class M, because of the definition of “school”. If the extension is to premises which have changed use to a nursery under Class S, it is not within Class M, because of the specific exclusion in Class M itself and in the definition of “school”. If the extension is to premises in use as a nursery, but not as a result of a change of use under either Class S or Class T, it can be within Class M only if the word ‘schools’ in Class M is to be read as incorporating nurseries. “

The judge decided that the use of the word ‘school’ did not include a nursery (para 18) and the judge decided the same applied for the GDPO.