In a report sent to clients on Tuesday night, Macquarie predicted a "further tightening in borrowing limits", pointing to the relative conservatism of banks in Britain and the US, which are generally prepared to lend 20 per cent to 25 per cent less to owner-occupiers than banks in Australia.

The Australian Prudential Regulation Authority has also conducted "hypothetical borrower exercises". In 2014 and 2015, it asked for serviceability assessments and used the results to call for lending standards to be tightened.

Between 2014 and 2015, APRA found the maximum loan sizes that could have been extended declined by, on average, around 12 per cent for investors and 6 per cent for owner-occupiers.

Cutting debt

Macquarie's research report this week also points to the likelihood of long-term de-leveraging by highly indebted households as being a significant headwind for annual credit growth – which it expects to run at around 2 per cent between 2019 and 2023.

The top 10 per cent of the most indebted households account for 45 per cent of total outstanding housing debt, Macquarie said.

"Assuming that over time those households reduce their debt-to-income level to around 5 times, from around 8 times currently, the level of system debt would reduce by around $300 billion, or 20 per cent," Mr German said. "We expect this to occur through a combination of ongoing reductions in borrowing capacity, disposal of assets and amortisation of debt."

After ANZ last week tightened standards on interest-only borrowers in response to APRA's new restrictions, Macquarie said the differential between principal and interest loans and interest-only loans for owner-occupiers is currently 55 basis points, and 46 basis points for investors.

But with minimum repayments for principal and interest loans being between 40 per cent and 50 per cent higher than for interest-only loans, there will be a "segment of customers that may not be in a position to to absorb a large increase in their minimum repayments," Mr German said.

"Some of these borrowers will not be able to eventually refinance into a new interest-only loan and will either need to dispose [of] assets, potentially putting additional pressure on house prices."