One question is; "Does 'DIY' gas installation represent a threat
to domestic gas safety?"

It's a loaded question.

Of course it does.

Just like drivers cause road accidents.

Th real question (along with Part P) should be, "Is there an
unacceptable number of accidents caused by DIY work?"

How would a CORGI installer know the answer to (either) question
anyway?

Only accident investigation statistics can tell if the problem is
significant.

Significant problem: Determine the best remedy -
education/regulation/inspection etc.

Insignificant problem: Do nothing.