This section deals with the time when an improvement notice becomes operative.
The general rule is that an improvement notice becomes operative at the end of the period of 21 days beginning with the day on which it is served under Part 1 of Schedule 1 (which is the period for appealing against the notice under Part 3 of that Schedule).
The general rule is subject to subsection (4) (suspended notices) and subsection (5) (appeals).
If an appeal against the notice is made under Part 3 of Schedule 1, the notice does not become operative until such time (if any) as is the operative time for the purposes of this subsection under paragraph 19 of that Schedule (time when notice is confirmed on appeal, period for further appeal expires or suspension ends).
If no appeal against an improvement notice is made under that Part of that Schedule within the period for appealing against it, the notice is final and conclusive as to matters which could have been raised on an appeal.