You can perform certain types of work without needing to apply for planning permission. All the information regarding your "permitted development rights" as well as a handy interactive house and guidance on common planning projects can be found on the Planning Portal.
If you do not need planning permission also called "lawful development".
* It is not a requirement to apply for a lawful development certificate however it is advisable as it is formal confirmation that the works/changes have been lawfully completed. This would show up on any property searches.