Hello Ian.
Danny's suggestion that it is permissible to install a gas appliance for your own use is fundamentally wrong.
The Gas Safety Installation and Use regulations, and ACOPS applies to ALL domestic and commercial premises. It requires that all installation, service, repair and removal of gas appliances and pipework systems must be carried out by a competent person. The authority for assessing competency has been granted to CORGI, thus fitters working in domestic and commercial properties must be CORGI registered.
The regulations do not differentiate between 'Own use' and other classes of use, thus it applies to ALL domestic gas systems.
Failure to observe the regulations is a Health & Safety offence and is governed by criminal law, and can carry a custodial sentence.
Danny!
How does a none qualified fitter know if the job has been done properly? It is unlikely that a home owner has the necessary equipment to perform the regulatory tests on the system, or to prove that combustion is within the specified limits. Failure to complete these tests and to record them is breach of the regulations, and has the potential to compromise safety.