The Local Planning Authority (LPA) will make decisions on a case-by-case basis as to what is the appropriate action that needs to be taken when a breach of planning control has been identified. This will be dependent on a variety of factors including the type of development the breach involves.
Depending on the route that the LPA chooses to take, there are different periods within which the person receiving the enforcement notice should take action. Some types of notices need to be acted upon within 21 or 22 days, whilst others will expire only after day 28. The notice sent by the LPA will clearly state the reasons for the notice and the timeframes within which appropriate action should be taken, as well as the consequences of inaction within the specified period.
You should NEVER ignore an enforcement notice.