Nationals Senator John Williams has added his voice to calls for Australia’s banking royal commission to be extended, despite the former High Court judge in charge of the inquiry wanting to wrap it up.

Labor wants the inquiry extended so more victims can tell their stories, with just 27 people having their voices heard out of more than 9000 submissions.

Senator Williams – who played a critical role inside the coalition to establish the royal commission – said the more witnesses Justice Kenneth Hayne hears from, the more he will reveal.

“I think commissioner Hayne could learn more by extending it and having more witnesses,” he told ABC radio on Monday.

“This royal commission is a one-off, we probably won’t see another one in our lifetime again. Let’s get it right, let’s do it right.”

Extending the inquiry would push it well into the next federal election cycle and allow whichever party wins government to deliver on its recommendations.

Treasurer Josh Frydenberg says if the royal commissioner needs more time he will get it.

“He has conducted a very rigorous, comprehensive and professional process to date,” he said.

Commissioner Hayne has highlighted an insidious culture of greed over decency permeating the big banks.

In a scathing three-volume interim report, he also criticised timid regulators for being far too soft on bad behaviour.

The commissioner has made it clear he does not want more time, declaring he must complete his job promptly.

However, the opposition is worried his interim report contained no draft recommendations.

Labor’s financial services spokeswoman Clare O’Neil says financial institutions and victims’ groups need time to discuss proposed changes to the sector.

“What is crucial is that we see proposals for reform that can be properly consulted on before the royal commissioner makes his final recommendations,” Ms O’Neil said.

“The interim report released on Friday makes it clear he is going to need more time to provide thoughtful, serious and significant recommendations for a sector we have been told is permeated by a culture of greed.”

Justice Hayne will hold one further round of public hearings in November to look at the policy questions that will be dealt with in his final report, due by February 1.

The next federal election is due by May.