Do I need to do some sort of course to use a camera while scuba diving? or is a normal PADI scuba diver certificate fine? Sounds a bit stupid..but thought it better to ask before spending £300+. Thanks!

No. An underwater photography course is intended to help you learn how to take better pictures sooner, but there is no reason that you HAVE to take a course to use a camera. There are no scuba police out there verifying qualifications. 🙂

Specialty courses are designed to accelerate the learning process, but trial and error is always an option. In some cases trial & error gives the test before the lesson, but with photography generally all you are risking is taking pictures you aren’t happy with.

Just watch your buoyancy while taking photos, many people get overly focused on the camera and lose buoyancy control.