Property prices could ultimately fall by 25 to 30 per cent from their peak, marking the worst downturn since 1890, according to an independent equity market analyst who has modelled the impact of tighter lending standards likely to result from the Hayne royal commission.

Douglas Orr of Endeavour Equity Strategy, last year predicted property prices would fall 20 per cent. But he has now downgraded his forecast based on the "new revelation" late last year that all, or almost all, mortgages written between 2012 and 2016 had used the Household Expenditure Measure to assess borrower expenses. He warned of a rise in loan defaults as recent buyers found themselves in negative equity.