There was a time when you had to do 80 hours per appliance, under supervision.. Gawd knows how you get 80 hours on hobs!
I've lost track of chapter and verse, but if you claim youre a plumber, have an rgi say you've done enough stuff with them supervising, then you do a bit of training in an ACS centre, like 2 days for CCN1 then get assessed.
First thing people fall over on is often a real live actual gas valve. If you've hardly ever seen one before and aren't sure what the various bits on it are, you're exposed. 4 slightly more than simple questions unanswered later, and the writing's on the wall. It's ok to have to look some things up, but not everything.