Hello Colin,
I understand your perspective on the issue, but this thread is only looking at work on gas systems which along with electrics I argue are specialist/public areas and need to be considered on their own merits rather than trying to generalise the concept of proving competence across all technical subjects.
I understand that contrary to your perception that Gas and Electrical regulations arose out of the industry trying to 'keep jobs for the boys' the history is that when the industry was in its infancy, there were multiple gas suppliers and no designed common standards between them, so an appliance designed for use with one suppliers gas, was not could not be used on another suppliers system. In some cases it would be could be explosively dangerous. There are very similar parallels with the electricity supplies and appliances.
If you are old enough to remember, this was one reason why you used to find to find the appliance manufacturers were also the electrical and gas suppliers.
The regulations/standards came about primarily to set out minimum standards of commonality between systems to enable consumers to mix and match suppliers and appliances. The regulations have been refined over the years to ensure that safety is maximised by forcing the adopting of best practice. As such these regulations should continue to be revised as its essential to ensure the compatibility of concurrent systems and where necessary the segregation of non compatible systems in a ordered and predictable way.
I believe this essential where the commodity has such potential to be publicly dangerous if managed incorrectly. Using an examples already used in the thread, there is a significant difference between trying to go SCUBA diving and working on gas systems. Essentially SCUBA diving is an activity which is a solo or small contained group activity, If an incident occurs, then it little risk to the public and only really affects those in the immediate vicinity. By comparison inadequate work on gas or electrical systems could be detrimental to unsuspecting users or works in the future.
As a professional, there was always a degree of concern when setting to work on a DIY system, as you literally did not know what you find, and as there is a duty as the last person to work on a system under the Reg's to leave it safe, which meant either being satisfied the whole system was up to standard, or sealing the system to prevent it from being used, and issuing a prohibition notice.
I am also very concerned (through experience of having to work on DIY messes in the past) that particularly in caravans and motorhomes, the carcass of the systems are subject to quite hostile environmental conditions, especially vibration. It seems incredible that installations in such adverse conditions are allowed to be completed by anyone, where as installations in good stable buildings are highly regulated for reasons of safety. Illogical.
I have come across,
Under sized carcass pipes for the duty of the appliances.
finger tight compression fittings,
Over tightened compression fittings with restricted gas flows and severed pipes.
Compression fittings with no olives, Plumbers White or PTFE tape used instead. One even used 8mm pipe into 10mm fitting using duct tape to make up the pipe diameter - which then leaked as the LPG dissolved the tapes adhesive.
Red rubber hose used to connect appliances.
bottle pressure LPG connected directly to the carcass (no regulator)
Flues disconnected, Balanced flues fitted through cavity walls with the transfer tubes omitted.
Flues rerouted with dips that collect condensate.
A Carver Cascade two fitted upside down!!
Corroded steel gas pipes repaired with duct tape.
I'm sure that most other professional fitters will have similar or worse tales of woe.
I have also worked on investigations into incidents, and it frightening to think that people carry out work on systems they don't understand with such devastating consequences. Even a highly qualified hydraulics engineer did some work on a gas heater in a caravan and nearly killed his wife and daughter, because he did not have the correct knowledge on how gas appliances needed to be flued.
LPG is a wonderful fuel. Used and managed correctly LPG is great, but misguided tampering through inadequate knowledge raises the potential for disaster to self and public to unacceptable levels.
Regulations are not to protect jobs for the boys, but to raise self and public safety when dealing with hazardous materials, and as such I believe and lobby should apply to ALL gas installations.