You will need to apply for planning permission if you wish to erect or add to a fence, wall or gate and:
it would be over 1 metre high and next to a highway used by vehicles (or the footpath of such a highway);
or over 2 metres high elsewhere; or your right to put up or alter fences, walls and gates is removed by an article 4 direction or a planning condition; or your house is a listed building or in the curtilage of a listed building.
the fence, wall or gate, or any other boundary involved, forms a boundary with a neighbouring listed building or its curtilage.
You will not need to apply for planning permission to take down a fence, wall,or gate, or to alter or improve an existing fence, wall or gate (no matter how high) if you don't increase its height. In a conservation area, however, you might need conservation area consent to take down a fence, wall or gate.
You do not need planning permission for hedges as such, though if a planning condition or a covenant restricts planting (for example, on "open plan" estates, or where a driver's sight line could be blocked) you may need planning permission and/or other consent.
Fences, walls and gates do not require building regulation approval.
Although building regulations do not apply, the structures must be structurally sound and maintained.
If the garden wall is classes as a 'party fence wall', and depending on the type of building work you intend to carry out, then you must notify the adjoining owner of the work in respect of the Party Walls Act etc 1996. This does not include wooden fences.
Garden and boundary walls should be inspected from time to time to see if any repairs are necessary, or whether a wall needs rebuilding. Such walls are amongst the most common forms of masonry to suffer collapse, and they are unfortunately one of the commonest causes of death by falling masonry. Your insurances may not cover you if the wall has been neglected.
Besides the general deterioration and ageing of a masonry wall over the years, walls may be affected by:
An increase in wind load or driving rain if a nearby wall is taken down.
Felling of nearby mature trees or planting of new trees close to the wall.
Changes leading to greater risk of damage from traffic.
Alterations, such as additions to the wall or removal of parts of the wall e.g. for a new gateway.