Give the Chelsea postcode, the side of the building and the reason for calling. Add safe photographs of the gutter and the approach below it. If you are asking about several runs, label the views front, rear or extension. Simple building descriptions are enough; you do not need to measure the channel at height.
Include the person who can provide access and any permission required. Mention pets, gates and stored items near the proposed working position. Ask what needs moving rather than trying to clear overhead obstructions yourself. If renovation has left materials around the route, cleaning after the building work is a separate room-cleaning request from gutter clearance.