Weighing in against the banks in the wake of Parliament's finance and expenditure committee's criticism of banks not passing on cuts in the official cash rate (OCR) to their mortgage customers, Bawden says the banks should be playing their part in getting the economy going again.

"You're not going to stimulate this economy until people start spending and if you don't reduce the costs of borrowing, you're not freeing up cash for people and businesses to do that," he says.

Making banks disclose their profit margins "is one way of keeping them honest."

Bawden says the indications the banks are treating their mortgage books as individual profit centres. Credit card interest rates haven't come down either. And there's also evidence the banks are taking a much harder line on charging fees.

While the banks are having to pay well above OCR levels on term deposits, they also get significant amounts of funding from non-interest bearing accounts, he says.

The OCR is currently 2.5% while Westpac, for example, is currently offering 4.25% for a 150-day term deposit. Westpac's six-month fixed mortgage rate is currently 5.39%.

While ANZ National Bank chief executive Jenny Fagg told Radio New Zealand her bank's first-half net profit was down about 30%, Bawden says that's because the bank chose to raise its charges against profit for impaired loans.

ANZ's latest general disclosure statement shows net profit fell 29.5% to $488 million in the six months ended June but charges for impaired loans jumped to $285 million compared with $96 million in the first-half last year. Excluding these charges, net profit would have been down 1.9%.