Alex the amount paid is calculated on Gross income but deducted from Net, so there are no tax advantages to repayment. It’s just method of collection.
So if your repayment was £100 a month then paying off early should mean you would get £100 extra in the amount you are paid into your bank account.
If it didn’t work this way then student loans would be much better and more advantageous for those paid more in higher tax brackets and that would obviously not be a good thing.