From 27 September landlords will not be able to use four types of state benefit income to reach the £25,000 threshold for borrowers.
The incomes that will no longer be recognised are: child benefit, child tax credit, working tax credit or pension credit.
Maintenance payments will also be excluded.
All full mortgage applications already submitted by 9pm on 26 September will not be affected by the change.
Any applications submitted from 6am on 27 September or where a material change is made to a previously submitted application will be assessed on the new policy.