Regardles of popular myth, folklore (or forum 'experts'), ALL gas work the UK in regulated. From an LPG perspective, the only task that can be performed by a non-registered individual (because it is not classified as 'gas work') is the changing of an LPG cylinder or the filling of an LPG-fuelled vehicle. All other 'gas work' can only be performed by a competent individual with the appropriate ticket((s) - ie: must possess the relevant ACS qualification(s).
Another myth is the belief that anybody can cobble together a gas installation and then ask a registered operative to 'sign it off' - if the work is carried out by a non-qualified individual, the registered person cannot 'sign it off' because selection of the components used in the installation, the construction methods employed and most importantly, the testing, commisioning & certification of the installation are ALL aspects that the registered individual states that THEY have performed themselves ...
I have seen some LPG installations on cars that are frankly beyond belief.
Very surprised that when I changed insurers the new lot were not interested in seeing any paperwork certifying the installation.
So in practice anyone can buy a kit off e bay and fit it. If they can get it to work then off they go!
I fitted mine myself, but only so far as installing the various components and the wiring. It was then taken back to the supplier for them to check, before then making the final connections and commissioning, testing and mapping the ECU. They then signed it off.
Not sure if this approach is entirely in accordance with the rules but I have known them for years, and they know the standard of my work.
One supplier I know now refuses to have anything to do with certification of anything unless they have done the entire installation from start to finish.
He got fed up with people bringing him stuff they had fitted where they had completely ignored all the various rules, despite him supplying pretty comprehensive details with the equipment. They then got very shirty when he refused to sign off the result. He had a very interesting catalogue of horror photos of some of the stuff he had been presented with, some of which demonstrated a level of stupidity that beggars belief.
My favourite was the guy with a toroidal tank fitted under the car so it was about two inches off the ground. Apparently he had asked for one that would fit in the spare wheel well, but then decided he didn't want to lose the spare wheel so simply bolted it on underneath!
A very common problem on cars is that every gas part inside the vehicle that might leak must be contained in a sealed housing with vent pies to the outside of the vehicle, so if there is a leak gas cannot find it's way into the car. Once installed the system should be checked to make sure it is satisfactorily sealed. Some people just don't bother at all, or seem to miss the point entirely with trunking that is not properly connected or with bits missing.
I have always thought that a gas converted vehicle should have to have the installation inspected regularly, either as part of the MOT or an annual check by a suitably qualified person. The latter probably being more practical as I dare say MOT testers already have enough to think about.
It should certainly be unlawful to drive a gas converted vehicle on the road without the installation being properly certified, but that is not the case.
Gas boilers are another example. Nothing to prevent anyone buying a boiler and installing it themselves, with potentially disastrous consequences. When we extended a previous property and needed a new bigger boiler I did much of the work myself, actually hanging it on the wall and installing the water pipes and flue. It was in a different location to the original one so it was pretty straightforward. My then Corgi registered mate came and disconnected the gas to the old one and connected up and commissioned the new one. Nothing to actually stop me doing it all myself if I wanted, and still the case today. Ok without a gas analyser you won't get it running as efficiently as it might but it will run. My plumber reckoned it would be fairly easy for the manufacturer to set it up in such a way that it wouldn't be possible to get it working without the proper kit. He had seen quite a few really dangerous DIY jobs and had a bit of a bee in his bonnet about it. This was many years ago, not sure how prevalent it is now.
I would have thought it would be simple enough for the manufacturer to determine what parts necessitate messing with the gas side, and for legislation to prohibit the sale of those parts, and the boiler itself, to anyone who isn't gas safe registered.
Seems simple enough.