What is the Law Concerning High Hedges?

There is one aspect of garden hedge keeping that is, unfortunately, increasingly common and increasingly controversial – the so-called ‘high hedge’ that annoys the neighbour.
Because of the increasing number of complaints, the problem has been defined in law – the Anti-Social Behaviour Act 2003: Part 8 (2005). Yes, Leylandii and other species have been given an ASBO! However, while national government has laid down broad definitions and guidance for local authorities, those local authorities still have the freedom to interpret them with an often generous degree of latitude, so if you are afflicted (or challenged), you will need to consult your local regulations as well.
We should start by looking at those definitions, such as they are:
A HEDGE: A hedge, at the simplest of levels is a “a line of two or more trees or shrubs” though the judge in a ‘high hedge’ case gave a little more detail: “A number of woody plants, whether capable of growing into trees or not, which are so planted as to be in line and which, when mature, to be so integrated together as to form both a screen and a barrier”. The law also recognizes a difference between an evergreen, semi-evergreen, deciduous or mixed hedge and acknowledges that a hedge planted on a slope may aggravate or lessen the problem.
A HIGH HEDGE: In law a high hedge is a) over 2m tall, b) generally completely or predominantly evergreen or semi-evergreen and c) affects the ‘reasonable’ enjoyment of a neighbour’s house or garden – this generally refers to a loss of natural light, though the legislation offers no guarantee of ‘uninterrupted light’. That a high hedge is blocking a view is a valid complaint but, by itself, is unlikely to be sufficient for the local authority to order remedial action
Before any official complaint is considered by the local authority, the complainant will generally be expected to show evidence (copies of correspondence, for example) that reasonable steps have been made to resolve the issue and to pay an up-front fee of at least £400. It can be acrimonious, time consuming and expensive to force your neighbour to bring their hedge down to size and even if you are successful, the local authority cannot order its removal or destruction and may determine that the hedge be reduced in a number of stages spanning a number of years. They may also delay the start of the work should immediate pruning be deemed to threaten the survival of the hedge or if there are birds nesting in it. Also, they may exclude specific trees in the hedge from the order.
Of course, the problem is entirely avoidable by ensuring that the right hedge is planted in the right place and is properly maintained.  let us once again state that the Leylandii makes a magnificent hedge but is not always a sensible choice for a high-density residential location.
One final thought: if you are buying a house and one of its boundaries is, according to the deeds, your responsibility and is defined by a hedge over two metres tall, you should dial in the cost of having it cut to an appropriate height. Equally, if the offending hedge is the responsibility of your potential neighbour-to-be, make formal enquiries before signing the contract. If you don’t, your new neighbours may well defend any subsequent action by the simple argument of ‘well, they knew it was there.’