My question was this, if you overpaid your interest over a number of yrs, say 5, at a rate of €500 per month you would entitled to 30k overpayment returned but if it was treated as an overpayment on the principal for 5 yrs it's potential impact is to reduce your mortgage by 50 - 60k, isn't it?
I'd imagine the banks don't want to do this but it starts to look more fair if they do.