Authorities in Australia and abroad are grappling with a new wave of low-tech terror attacks by extremists who had largely been deemed low risk.

The attackers behind the Westminster Bridge car attack and last weekend's London Bridge van and knife rampage had been investigated by authorities but had dropped off intelligence radars.

It was a similar story with Brighton siege killer Yaqcub Khayre and Lindt gunman Man Haron Monis, who were not deemed priority targets when they turned violent.

In an interview with Fairfax Media, NSW Counter Terrorism Minister David Elliott said he was talking to the private sector "because the government can only monitor so much".

"What has concerned me is that, in most of the case studies in the last three years, the people that have been the offenders have been known to authorities, however they have actually been at the lower end of the list," he said.

"In the case of the Westminister Bridge attack, the offender was at the lower end of people being monitored but he had hired a car for seven days which wasn't returned, he'd bought two very large carving knives. So his face to face exposure was actually with the non-government sector in the lead-up to the offence."

Mr Elliott said the airline industry and the finance industry do a "brilliant" job of monitoring concerning activity.

"But it's quite clear that we're going to probably need to expand the net when it comes to monitoring in the non-government sector," he said.

David Wells, a former Australian intelligence officer working as a private consultant in Britain, agreed that security agencies need outside support.

He said it is impossible for agencies like ASIO to have watching briefs over thousands of people and investigators instead triage leads based on whoever appears to have the intent and capability to do something at that point in time.

However, he said airlines and finance companies have had long-standing co-operation "based on known modus operandi of terrorists".

If, for example, truck and car rental companies started attracting the attention of authorities, attackers would simply change their way of doing things, he said.

"There's a lot of mitigation that could improve the general things slightly ... but, in my view, even if individual errors have been made in the triage process, there isn't much more you can do with the UK and Australia law enforcement that we haven't already done," he said. "People are looking for solutions but it's a very difficult problem we're facing for a long time."

The idea has gained traction in the US, with the Brookings Institution think-tank saying earlier this year that the private sector holds the most untapped promise.

"The business case is compelling: violent extremism poses a clear threat to companies, employees, and customers. Terrorism severs supply chains, drains local labour pools, and shakes investor confidence. The economic costs of terrorism reached $89.6 billion in 2015," authors and counter-terrorism experts Eric Rosand and Alistair Millar wrote.

However, they said most business owners are unaware of what they can do or too risk-averse and nervous to get involved.

Mr Elliott said he intends to discuss his plan with various chambers of commerce, industry associations and the federal government. He has had preliminary discussions with Premier Gladys Berejiklian.