Mr Howard, who famously declared in office interest rates would always be lower under a Coalition government, said the economy had changed since he led the country.

"The progressive reduction of interest rates, in the circumstances where there seems to be a large amount of liquidity in the system, does not appear to have had the sort of impact it might have had on economic activity five or 10 years ago," he said.

"We are, in my view, living in certain uncharted waters and an unpredictable environment."

Mr Howard addressed a booked out crowd at the National Library of Australia on Wednesday, a day after the Reserve Bank lowered interest rates to their lowest levels since the 1950s.

The cut came as the central bank downgraded economic forecasts for the coming financial year, saying the economy will be weaker and will take longer to recover than previously thought.

While Prime Minister Tony Abbott has seen rates fall by 0.5 percentage points in his 19 months in office, rates fell from 7.5 per cent to a low of 4.25 per cent in the first half of Mr Howard's leadership, before 10 consecutive rises - including one weeks before the 2007 election - left the official rate at 6.75 per cent when he lost office.

Delivering the Sir Roland Wilson oration, honouring Australia's longest serving Treasury secretary, Mr Howard said major economic reform was now harder to pass through the Senate but would occur when it was seen by the public as fair and in the national interest.

"The fact [my government] were able to see 80-85 per cent of our reform package delivered through negotiation with the Australian Democrats was very important," he said.

"I would be very surprised if it's possible for the Coalition government to negotiate major economic reforms with the Australian Greens."

"[But] I think it stands beyond argument, at some point we must return to taxation reform, and return to industrial relations reform."

The Liberal PM and Fraser-era treasurer would not comment when asked whether there should be changes to the GST he introduced.