.......for which I suspect you'd find it difficult to get cover unless you had Yachtmaster or equivalent, or lots of vouched-for experience.
Also DOT (I think?) charter coding for the boat.
Lots of risk assessments
Dunno after that but I bet there are other things. And lots of inessentials that would catch you out if something went pear-shaped. F'rinstance: your guests succumb to food poisoning en voyage after sampling your boil-in-the-bag casserole. "So, Mr X, you have a Food Hygiene certificate, don't you"? "Err... no".
Cynical? moi?. But I've no doubt that, to be a successful charter skipper, you need to be the kind of person who isn't put off by the obstructions of grinding bureaucracy. Go for it!
To charge people money to take them to sea you need a minimum of a Coastal Skipper ticket with a commercial endorsement. That's the easy bit, just pay your money and take the exam . . . probably better to go straight for YM, you might want to do a week's preparatory course first with a reputable sailing school. For the commercial endorsement you need a certificate to say you have done a sea survival course, plus a medical. You must already have a current First Aid certificate to sit the exam.
The boat must be coded - which can be expensive. You might need a new gas installation, new liferaft, lifejackets etc, plus an annual inspection. Your boat might also need structural work to make it compliant, although this is less likely.