Amandini,
You don't have to have your certificates for the assessment day, I took mine along but I wasn't asked for them. I think they require to see them if you are going for CSA (customer service agent.) Let us know how you get on.
Brightonflyer,
What a positive post! How nice to hear that you are enjoying your work...so many people seem to think that a transfer to LGW is a bad thing... my niece used to work as cc at LGW and loved it. (She is now management, so it just goes to show that if you want to get on in BA, you can, and excuse the pun, the sky's the limit!)
I've said this before - the job is what you make it. Do the job you were employed to do to the best of your ability, and it will reap rewards.