Have you already studied a year at university (i.e. are taking a year out in the middle of your degree) or just have a deferred place for next year?
Assuming the former, ask your tutor at university to write your reference. Unless you intend to return to your university to complete your degree before starting a second one at this other university, you will not have any predicted grades - they will discuss in the reference stuff like how well they thought you worked, how well you integrated into university life, how well suited they think you are for a different university, any extenuating circumstances or factors which may have influenced your decision to start again at another uni, and perhaps why you did this gap year/ what you have gained from it, etc. There is no requirement for them to submit predicted grades unless you are due to sit some exams at your current uni before you start again at the new one.
EDIT: ok, just read your latest post. In that case, you CANNOT apply to other universities while holding a deferred place elsewhere - you have already committed to the other university. It is not possible to apply via UCAS without rejecting your current offer - the system will not let you do it.
What you can do is turn down your current offer and reapply during your gap year. You should ask your tutor from sixth form to write your reference - they will probably just update the one they submitted last year. There is no need for them to submit predicted grades unless you are taking any additional exams/ retakes during your gap year.