Most planning applications are decided within eight weeks, unless that is they are very large or very complex - in which case the time limit is can go to 13 weeks. In all cases, the authority in question should be able to give you an idea about the likely timetable. In cases where it cannot decide your application within eight weeks, it should always obtain your written consent to extend the period. If it has not done so, you can appeal to the First Secretary of State.
However, as such appeals can take several months to decide and it is normally quicker to reach some agreement with the LPA where ever possible.
If a local planning authority turns down an application or allows it with conditions which the applicant finds unacceptable, the applicant can make an appeal, so that the matter can be resolved by a Planning Inspector. An appeal is also permitted on the grounds of 'non-determination' when the local planning authority fails to determine the application within the statutory period. Very occasionally the First Secretary of State will take such decisions.
An appeal is, however, a last resort. Agreement can often be reached with the planning authority following discussion of the reasons given for the refusal and adjustment of the proposal.
The appeals process can be long, so it makes sense to try to avoid any issues in the first place. This in turn means that a great deal of research should be carried out before an application is made. This should include checks on Land Use Constraints , Flood zones, points of interest and special scientific interest etc. All such matters must be carefully considered before any application is made.
For some information on Planning Matters please see:-
Maps for Planning Applications
Planning applications and how they are processed
Planning Applications – Who Is involved
Planning Applications - When do you get a decision?
Planning Appeals and other casework