There is no national average in terms of successful planning appeals as it varies greatly across the different boroughs and Local Planning Authorities (LPAs). However, the percentage of success rate could fall somewhere between 10%-30% based on previous records. This rate has tended to remain fairly constant through the years.
Appealing should always be the last resort when your planning permission is not granted or if certain conditions have been put on your application, which you are not happy about. Speaking to your local planning authority should be your first step.
Sometimes, amending your application with some changes to your proposals wins you the acceptance of your application. With quite a low rate of successful appeals, appellants should make sure they feel be confident at the time they make their appeal that they are able to make their full case. A planning consultant may help with the smooth running of your project and guide you on any appeal processes that may arise.