How is property income calculated for supporting application purposes

I am the parent of someone, making a supporting application for finance loan. I have property income, however with the new rules on mortgage interest payments, the income HMRC have is higher than my actual income. For tax credits purposes, they use the net figure after mortgage costs, so this is what I used for the supporting application for student finance, but there is a variance (which I can demonstrate in my tax return as being the mortgage interest payments). Please advise, because my actual income is the lower figure, and it affects bursary that my daughter could be awarded at the University as well as the amount of the loan. thanks

Thank you Isaac, so in summary and clarity, the figure student finance use for property income is the net profit figure after all costs and expenses including mortgage cost interest payments. So to evidence this, I can send my tax return with the property income and expenses and finance costs shown, to highlight and evidence this variance. And Student finance will use the lower (net profit) figure as income amount. thank you Lesley