The estimate, in a report by a leading watcher of the Four Pillars, came to light yesterday as two more financial regulators called for an investigation into the record margin between the Reserve Bank of Australia's official interest rate and the price of paying with plastic.

In a report previously only available to well-heeled clients of investment bank JP Morgan, top analyst Scott Manning said ANZ, CBA, NAB and Westpac collectively earned $920 million annually from credit cards in 2012-13. The report said the majors’ average margin on credit cards had approached 10 per cent in that time, up from less than 7 per cent in 2007-08.

However, Mr Manning yesterday told News Corp Australia the margin on credit cards was now as much as 16 per cent — money sourced at 3 per cent was being lent out at 19 per cent.

The margin on mortgages was 1.2 per cent, he said.

In his report Mr Manning estimated the top quarter of credit-card customers each earned a bank nearly $800 of profit. The worst quarter cost the bank about $400 each.

He noted the most profitable customers were not the “highest quality”. Those in the middle were. Mr Manning estimated the banks’ “return on equity” from such customers was nearly 150 per cent. In other words, for every $1 of funds employed by the bank, it reaped $2.50.

“These customers provide an attractive mix of characteristics from ... a relatively high source of transactions and volumes, alongside corresponding interest income. However, they also see relatively low impairments”, or losses, Mr Manning wrote.

Meanwhile, the Australian Prudential Regulation Authority and the Australian Securities and Investments Commission yesterday joined the RBA and Federal Treasury in advocating for an investigation of credit card margins.

“Is it something that ... we think is worth looking at? Certainly,” ASIC deputy chairman Peter Kell told a Senate Budget Estimates hearing in Canberra. “We would be very much prepared to work with Treasury to look at this issue because it is obviously something of community concern.”

APRA chairman Wayne Byres told the hearing: “The margins on credit card business look very high certainly to any other form of credit, and certainly I can’t sit here ... with an explanation of why that is. So, to that extent, informing us all about that is probably a useful piece of work.”