@LM1996
Last year I was in the same position as you appear to be, in year 13/ upper sixth applying for the FPP. When it came to filling out my details however, there was no option for predicted grades. I queried this by emailing BA and they told me I must already have the grades upon applying, and so I had to withdraw my application. As they said to me, this isn't what you want to hear I'm afraid, but I would still apply this year with this in mind if I were in your position, just in case the rules have changed. I hope this helps.