In an ideal world, the redress where property prices have increased should be that the bank is forced to make an offer to the client of either
The bank purchases the same house, or a very similar one in close proximity.
Or
If the customer has been forced to move, and wants to stay in the new location, the bank should pay the current value of the lost house towards the purchase of a house in the preferred location.
On top of that, the bank should then
give a mortgage on the conditions that the original one should have been on, with the same remaining balance
Refund any difference between rents paid, and the mortgage payment