They want someone to invigilate the exam. That is reasonable, particularly since it appears as though in-person exams are still available.

I'm not sure what the situation is in GB but, in Canada, the question bank (and answers) were publicly available from the licensing body when I took my exam. Under such circumstances, it would be trivial to cheat. (It was also quite handy. I made an online test generator for the club I belonged to so people could take practice exams to figure out when they were ready.)