Use Class A3 (restaurants and cafes) comprises use for the sale of food and drink for consumption on the premises, i.e. restaurants and cafes.
Use Class A3 (restaurants and cafes) benefit from a variety of different permitted development opportunities to change use without requiring a full planning application. There are a number of conditions and limitations to such a change however, and further detailed information about this can be found here on the Planning Portal website. This website also details other restrictions to permitted development that may be in place, such as planning conditions or Article 4 Directions, and it is recommended you get confirmation from the local planning authority about changes of use proposed using permitted development rights.
If an A3 premises does not benefit from permitted development rights, planning permission may be sought to change it to another use. You can learn more about this process here.