In England and Wales work carried out on a part of your property which adjoins your neighbours, must comply with the Party Wall Act 1996. This covers any wall on the boundary line of two or more properties and includes garden walls as well as the walls of buildings.
All work which might have an effect on the structural strength or support function of the party wall or might cause damage to the neighbouring side of the wall must be officially notified to the affected neighbour. You must serve the notice at least two months before the intended start date of the work, giving details of the work to be carried out. No work may start until all neighbouring parties have agreed in writing to the notice.
It is normal practice to record the current state of neighbouring properties and inspect again for damage at the completion of the work. You are responsible for making good any damage caused by your work.
If in doubt, seek advice from your building control office, a party wall surveyor or an architect.
Although Scotland and Northern Ireland are exempt from the Party Wall Act 1996 you should check for any restrictions with your local planning department.