I have a junction box in a doorless porch. It serves a fan in an adjacent bathroom, and a shed by an overhead line which has a light and a couple of power points for minimal usage. It is an individual circuit connected to a consumer unit with its own 16amp MCB. I want to create a spur a short distance away to a weather proofed socket outlet. This will be used for ordinary gardening tools. Am I allowed to fit this myself?