You do not need permission to plant a hedge, as the usual planning rules that restrict the height of boundary walls and fences erected around gardens do not apply to hedges. And, until 2003 there was no legal restriction on how high a hedge can grow.
A natural hedge can be an attractive feature in any garden. They are relatively inexpensive to create and have many positive benefits. A properly maintained hedge can help provide screening for both privacy and security. They can also create a habitat for wildlife, as well as marking the legal boundary between two adjoining properties.
A neglected hedge can, however, cause problems to a neighbouring property, especially if its height is allowed to grow unchecked. The commonest concerns are the loss of light to windows and gardens of houses that are situated close to the boundary where the hedge is growing.
Following calls from the general public for help to control the nuisance that overgrown hedges can cause, the government introduced legislation under Part 8 of the Anti-social behaviour act 2003, to tackle the problems specifically caused by high hedges. You can download the council's policy on high hedges, and the form to make a complaint.