We work inside your own property, up to your own meter and your own consumer unit, and no further. A shared riser, a building's main board, a roof tank serving several flats and a pump on a common line are all outside it.
This is not caution for its own sake. Those things belong to a building rather than to a flat, and a tradesman who works on them at one owner's request can leave eleven other flats without water and one owner with a bill nobody agreed.
Get written permission from whoever runs the building and we will do the work the same week. If you do not know who that is, tell us and we will usually be able to say, because we have been in most of these buildings.