I only know how ELECSA do it but I think they are all much the same. There is a list of certain requirements you need to see if you have them all covered. Have a look on their website for the list. You will have seen from the threads that most of us do not look forward to annual assessment. Most look for C&G Testing Cert, you must have the test meters / a job to show them / regs / On Site Guide / complaints book / evidence that you issue quotes / invoices etc.
I think the crux is that you need to demonstrate that you are competent to do and test domestic installations. Just keep mugging up on testing , I think they all get you to demonstrate a test on site . Oh you need test results for any jobs you have done .
Don't worry about it , you can always go for it again when you feel more confident and don't forget, they actually want you as a member . You could well get through with a list of non compliances to comply with, like " should issue quotes/ invoices/ testers should have recalibration certs etc.
I'm not the most confident tester either, specially with the assessor whatching, I'm fine on my own.
Deke
England 2 Germany 1