I do cold & hot, sinks type waste and some ancillary bits often and have the plumbing cover incl hot work on my insurance.Mind I also have a "pet" plumber, who I try to get to do these things.
The biggest workload in this area is for one customer who have just swapped their spec from soldered copper to push fit PE-X (XLPE to us!) & solvent weld ABS or PVCu, with solvent weld waste staying.
So I may not be using the plumber so much, I use him for these jobs as I HATE soldering pipes.
Haven't done any oil work for 20+ years and now the regs have changed.
Last time I did gas CORGI was not compulsory in our situation.
Mind how many Corgi registered plumbers could work on an automatic natural gas carburettor with 6" bsp ports!
We used to test for leaks on the carburetted gas lines with a flame torch, much quicker.
Now a test, think about it.
This is your starter for 10.
Which is most dangerous, testing for leaks on a pressurised pure gas pipe line or a pressurised carburetted gas pipe line with a naked flame and why?...