You'll need to apply for planning permission if you wish to erect or add to a fence, wall or gate in the following cases.
You do not need planning permission to take down a fence, wall or gate or if you wish to make any alterations to an existing fence, wall or gate as long as you do not increase its height.
However, you might need consent to take a fence, wall or gate in a conservation area.
You don't need planning permission for hedges although if a previous planning condition restricts planting a hedge (for example in 'open plan' estates or if a hedge restricts a driver's view), you may need to get permission or written consent of a different nature.
Source: www.planningportal.gov.uk