"I would urge you to consider that there have been failures offline since we have had humans," he said.

"I don't think we should looking for a bullet-proof system because there is none."

Mr MacGibbon was former head of the police's high-tech crime centre and was the government's cyber security adviser.

The best way to verify age was using biometrics - essentially a selfie, which would allow sites to verify age without accessing people's data, and would stop children using their parents' identification to go online, he said.

"We do need to take action," Mr MacGibbon, said. "We owe it to the people of Australia to reflect Australian values online."

Mr MacGibbbon, who now works in private cyber security, was speaking to a parliamentary hearing on age verification for pornography and gambling.

People were willing to accept flaws in regulations offline but not online, he said.

"We accept that seatbelts save lives, but not every life. But we still mandate the wearing of seatbelts.

"When it comes to online regulation or online intervention or online behaviours, there is a prevailing philosophy that says that everything should be perfect or you should do nothing - and if you do try to do something it will be completely ineffective anyway and as a consequence let's just leave it to providers to work out amongst themselves. And I think we see the consequences of that market failure today."

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Efforts to limit access to online pornography for children are seeing pushback from people worried about privacy and data safety.

But Mr MacGibbon said while risks were higher online, people risked privacy and anonymity in the offline world also. If an adult was entering a 18-plus physical site, they faced the potential of being seen or a "bored hacker" trying to stream video from security cameras.

Effective online systems would use biometric data to verify age, to prevent children simply accessing a parent's driver licence or other identification.

The face verification system being developed by the Department of Home Affairs could verify age without people having to provide data to pornographic or gambling websites.

The user would present their face to a computer camera.

"You could have a traffic light type system to providers that basically either gave them a green light that says the person standing in front of this camera is of age and has government documents to prove it, or a red light which would either indicate that there is no documents to verify against my face or that I am under age.

"The benefit of that type of system, and I'm not necessarily advocating for it, is that you wouldn't have to pass any details on to the provider ...

"I'm not suggesting necessarily that that's a great solution and I can hear privacy people already saying that that would be hugely problematic. But it's the only way I can think of actually creating a system that allows you to have your ... biometrics compared to documents that the government holds and then provide some form of green light or red light to a provider."

In Britain, the age-verification proposal would block websites' access to credit cards if they didn't comply.

Mr MacGibbon said the same could be done in Australia. Websites could also be blocked at border routers. While neither was perfect, and there was a risk also that people would be driven to darker corners of the web to avoid age verification, he urged the parliamentarians to take some action.

"There are technologies sufficient to provide services to the vast bulk of cases when it comes to online wagering or access to legal yet restricted pornographic material. Whether you could guarantee its safety and privacy would be a bridge too far, but then again banks get robbed offline and documents get stolen offline. I've grown up in a world of policing that says that the system will fail everyone at some point."

Hackers, whether criminal or state, would be more interested in health records, tax records and passports than exposing people for pornography or gambling, he said.

"We shouldn't be seeking perfection, we should be seeking things that take us closer to our offline lives."

Australia had for a long time convinced itself it could do nothing online and taken very little action, to the detriment of society, he said. Australia was "very immature" about online behaviour, using the cloak of anonymity, and should better enforce its values online.