Repayment rate for a second student loan?

I already have a student loan and am meant to repay 9% of anything above £25,000.

I know that if I took out a postgraduate student loan, I would repay another 3%, so it would be 12% of anything above £25,000

What if I take out a second student loan for a healthcare degree? Would it be added to my existing student loan amount or would I pay 9% + 9% = 18% of anything above 25,000?