Criticism of the big four banks from Treasurer Josh Frydenberg and Reserve Bank governor Philip Lowe has been vindicated by competition tsar Rod Sims, whose investigation found lenders did not reduce mortgage rates quickly because they wanted to hold onto revenue.

The Australian Competition and Consumer Commission also found mortgage holders who stick with their lender are thousands of dollars worse off due to higher variable rates, with new customers on average charged 0.26 per cent less than existing home loan holders. Long-term customers who have had a mortgage with the same lender for the past five years typically pay 0.4 per cent more than new loan holders.

ACCC chairman Rod Sims. Credit:AAP

"I just want [consumers] to know this - If you haven't rung your bank up in the last couple of years you're probably paying too much," Mr Sims said.

In June 2019, Mr Frydenberg urged the banks to pass on the RBA's 0.25 per cent rate cut to home loan customers in a bid to drive unemployment down towards 4 per cent and publicly heaped pressure on the major financial institutions. The RBA's minutes at the time pointed out that funding costs for the banks were at record lows and there was no impediment to passing on full cuts.