Mains 220-240v AC systems: Essential! All additional permanent wiring, with the exception of very minor work, must be notified to the local Council building control department, or an electrician who is registered with one of the Government-approved “Part P” schemes must carry out the work. This electrician will then take care of all of the necessary procedures and will provide you with a certificate that confirms the work meets Building Regulations / BS 7671. It is best to find an electrician who is experienced in outdoor installations as they can be more complex than indoor and involve armour plated cable which is more complex to work with than normal household wiring cable. If installation is carried out by somebody who is not a registered competent person, the use of registered third party to certify notifiable electrical installation work is acceptable as an alternative to using a building control body for the entire installation.
Some minor work outdoors, such as replacing an outdoor light which is already connected to an existing circuit, is not currently notifiable (June 2016). Local Council will always be happy to advise whether or not specific work is notifiable so do check if in doubt!
12v AC systems: Recommended to use a qualified electrician but if the lights are not permanently / directly hard wired into the house wiring circuits then it is permissible for a DIY installation. To qualify for a temporary installation, the transformers must be able to be unplugged from the external waterproof sockets, or an indoor socket such as in a garage or shed. Any mains outdoor waterproof sockets must be installed by a qualified electrician.