If I apply for an integrated foundation course, can I switch on results day?

Do you mean that you have already applied, and you are holding an offer for a Foundation year?
Or have you not yet applied anywhere?

i haven't applied anywhere yet, just trying to understand all my options

Your chances of finding a Foundation year for Physics in Clearing are slim.
Universities usually back-fill any gaps with applicants who missed their grades on their main degree.
Why have you left it so late.

I’m not talking about clearing, I’m in year 12 lol
thats why I said if I’m applying for such a course if my predictions end up low
I just want to know if I apply for a physics with foundation year course and get accepted, would I likely be able to switch to just physics if my grades are fine??
The entry requirements for the foundation year courses are lower.
I’m expecting predictions of around AAB ABB so this is me trying to understand all options as my school doesn’t budge from predicted grades.

Many unis will make this swap automatically (FY > main prog) if your actual results are decent enough.
It’s an import question to ask before you apply.

Its possible, but of course it would still rely on there being spaces on the main degree course.

If my predictions somehow end up rlly low il apply for physics bsc with a foundation year, but if my actual grades are way better, can I switch?
Thinking of unis like Nottingham, Manchester and Holloway which offer these