City school having to cover D-day (8)
I believe the answer is:
edmonton
'city' is the definition.
(Canadian city)
'school having to cover d-day' is the wordplay.
'school' becomes 'eton' (famous UK public school).
'having to cover' is an insertion indicator.
'day' becomes 'mon' (abbreviation for Monday).
'd'+'mon'='dmon'
'eton' enclosing 'dmon' is 'EDMONTON'.
(Other definitions for edmonton that I've seen before include "Capital of Alberta, Canada; North London area" , "Part of London (or Alberta)" , "Tom Donne is out in the Canadian city" , "Canadian city - region of London" , "Canadian provincial capital" .)