Pretty stupid - I don't know who is telling them?
Think of all the visitors to a school site, as elsiegee40 points out. They're always accompanied if they're going about site. Often we have external speakers in to speak to students - I don't know if they're CRB checked or not but they're always accompanied and in a hall with a huge number of students and staff to.
Isn't there a new "ISA" database coming in in September - which, apparently, the employee has to pay £60 to register for? Obviously a system designed by someone who thinks £60 is, to borrow a phrase from Boris Johnson, "chicken feed".