I used went on maternity in March and used my P60 net figure
It doesn’t really matter for the application as you still get paid the same amount, you would just need to pay a high income tax charge on a tax self assessment if you’re adjusted net income is above the threshold. To be on the safe side I would put it as if you’re in full time employment x
I think still put down as if still in full time employment but if anyone else knows for sure , feel free to correct me!