Did you know planning rules have relaxed? In most cases, you can go out three metres under permitted develop laws.
Advise them of your planned development
If your neighbours raise any concerns or objections, the local authority will decide if their objections reveal any impact on the amenity of the neighbouring properties and whether your plans can go ahead.
They derive from a general planning permission granted not by the local authority but by Parliament. Bear in mind that the permitted development rights which apply to many common projects for houses do not apply to flats, maisonettes or other buildings. Similarly, commercial properties have different permitted development rights to dwellings.