If you are invited for an assessment with BA, you will be expected to take your certificates with you on the day. They will check these and take copies of them before you are interviewed. On the day I went, two people were asked to leave straight away - one girl forgot to bring her certificates and the other girl didn't have the necessary grades even though she said she did on the application form. The recruiters check everything!
Hope this helps.
PS If you don't have your certificates, you can request copies of them from the exam board (although I believe there is a fee for this).