All jokes aside James - if you know your stuff you'll be ok. As stated in a different thread, I've got mine in Feb and I'm a bit nervous, but it's only natural.
Brush up on building regs issues that apply to your work and testing correctly and WORKING SAFELY!!!
Don't worry yourself about it, I've had nothing but good experiences with all my assessments. There are times you know when the assessors know less than you. They're not there to trip you up they're there to help you. Remember it's not in their best interests to upset you in any way.