Adding a socket is more than connecting wires. We check the existing circuit first: whether it's a ring or a radial, whether it's already overloaded with spurs, and whether it has RCD protection. BS 7671 requires 30 mA RCD protection for socket outlets rated up to 32 A, and for cables buried less than 50 mm in a wall. If your circuit isn't RCD-protected we'll explain the options, which range from an RCD socket to a consumer unit upgrade.
New cables run within the safe zones, vertically or horizontally from an accessory, so whoever hangs a picture or a shelf later knows where not to drill.