In the case of shotguns you should hold a valid shotgun certificate. You may also attend with a shotgun loaned to you by another certificate holder under the 72 hour rule.
In respect of rifles. You must hold a valid firearm certificate authorising the possession of the rifle. The conditions on the certificate must authorise the use of the rifle at the training venue for the purpose of the course (either target shooting or live quarry and zeroing – dependent upon the course). If your certificate restricts where you can use your rifle (the closed condition) you will not be able use it on a course.