Ideally, this can be done by a standing agreement between the main creditors, and there have been moves in this direction.
Failing that, the PIA is the fall-back route to this when it proves impossible for the main mortgage creditor to ensure (in cooperation with the other creditors) that, taking a holistic view of the borrower’s position including other indebtedness, the entire debt is sufficiently restructured. Even before the emergence of arrears, there are usually warning signs for problem loans.