A former head of Britain's MI5 cracking down on online encryption could lead to more illicit hacking.

Lord Jonathan Evans, chief of the MI5 spy agency between 2007 and 2013, individuals and businesses should be allowed to access important cyber security technology.

“My personal view is that we should not be undermining the strength of cryptography across the whole of the cyber market because I think the cost of doing that would be very considerable,” Lord Evans has told reporters.

“I think if you don't have secure encryption, it makes it easier for the hackers.

“It means it's easier to get into financial services, into people's private emails, into their own messages when there isn't lawful authorisation.”

But in Australia, the Turnbull Government wants tech companies to be forced to hand over encrypted messages, with legislation on the way that could mimic British laws introduced in 2016.

When the UK legislation was still being debated, Apple chief Tim Cook warned of “dire consequences”, opening back doors to devices hackers would be unable to resist.

Lord Evans politicians wanting to stop terrorists who use encryption need to be aware of competing interests.

“On the one hand, there is a general consensus that with appropriate lawful authorisation, it's right that the government or government agencies can access the communications of those people who cause a threat,” he said.

“On the other hand, there is also a very strong public interest in ensuring that we have cyber security so we can live our lives on the internet, so we can undertake our business activities on the internet.”

But the former spy boss says tech companies also have a responsibility to work with intelligence agencies.