As an income booster, you are on the mortgage alongside the homeowners and are jointly responsible for the mortgage loan and the monthly repayments.
This means that if you apply for another mortgage, the full Gen H monthly mortgage payment will be taken into account by the lender.
When you apply for a mortgage, lenders look at your income, expenditures, credit history and existing credit facilities/debt to assess your affordability. Therefore as an income booster, the remaining Gen H mortgage balance will appear on your credit report, even if you are not contributing to mortgage repayments.
Something to bear in mind is that an income booster does not need to be on the mortgage for the full term and can be removed after a fixed rate period comes to an end subject to the home owners being able to afford the mortgage on their own.