How big can you build a wall without planning permission?

In the UK, you can generally build a wall up to 1 meter high at the boundary of your property without planning permission, or up to 2 meters if it's set back from the boundary. However, there are exceptions, such as if your property is adjacent to a highway, where the maximum height is reduced to 1 meter. It's important to check local regulations and any specific restrictions that may apply to your area. Always consult with your local planning authority to ensure compliance.