Ladar Levison, who ran Edward Snowden’s email account, said moves to allow government access to encrypted data would weaken safety online for everyone

British prime minister David Cameron’s calls to stop tech firms from protecting their users’ information with encryption technology are “insane”, according to the man who once ran NSA whistleblower Edward Snowden’s secure email account.

Ladar Levison, founder of the encrypted email service Lavabit, made his comments as Cameron lobbied Barack Obama to press US technology companies to give law enforcement greater access to encrypted communications, following the deadly attack on the Paris office of the magazine Charlie Hebdo. Before a joint press conference with Obama at the White House on Friday, Cameron said internet firms “have a social responsibility to fight the battle against terrorism”.

Encrypted messaging services have become increasingly popular in the wake of the Snowden revelations. The latest versions of Apple and Google’s mobile operating systems are encrypted by default. Other popular messaging services such as WhatsApp and Snapchat also use encryption, and security experts are pushing for more.

Levison, a leading proponent of encryption technology, joins a chorus of critics who have called Cameron’s proposals unworkable and dangerous.

“David Cameron is insane if he’s serious about giving the government the capability to snoop on everyone,” said Levison, who shut his email service rather than hand over user data to US authorities.

Levison said moves to allow government access to encrypted data would weaken safety online for everyone. “Think how much information has been stolen online already in the last year,” he said, referring to the hacks of Sony, Target and Home Depot. Creating “backdoors” for US or UK authorities would make the entire system more vulnerable, he insisted.

“Encryption underpins the entire network of trust on the internet, from downloading applications to banking and software updates,” said Levison. “If you have to hand over the keys, you’d be well advised not to use some services,” he said.

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Levison’s comments came as the Guardian published details of a newly uncovered 2009 document from the US National Intelligence Council that called encryption the “best defence” for computer users to protect private data.

The report warned that “almost all current and potential adversaries – nations, criminal groups, terrorists, and individual hackers – now have the capability to exploit, and in some cases attack, unclassified access-controlled US and allied information systems.”

Despite the report’s conclusions – and the massive hacks of major companies – the increased use of stronger encryption techniques by tech companies since the NSA revelations has caused increasing tension between the US and UK authorities and Silicon Valley.

Last November, the newly appointed GCHQ spy boss, Robert Hannigan, said US social media giants had become the “networks of choice” for terrorists. His comments came in the wake of criticism from the FBI director, James Comey, who said: “The notion that someone would market a closet that could never be opened – even if it involves a case involving a child kidnapper and a court order – does not make any sense,” said Comey.

Leading up to his visit with Obama, Cameron has stepped up his calls for greater access to encrypted information. He said the UK “must not” allow means of communications that cannot be decoded by law enforcement. “The attacks in Paris demonstrated the scale of the threat that we face, and the need to have robust powers through our intelligence and security agencies in order to keep our people safe,” he said.

“The rallying cry is that we have to stop terrorism. Everyone hates terrorism,” said Levison. “The only thing we hate more than terrorism is hurting children. Whenever they want additional authorities, these are the issues they put on parade,” said Levison.

“It reminds me of that quote from Benjamin Franklin: ‘Those who surrender freedom for security will not have, nor do they deserve, either one.’”

Chris Soghoian, the principal senior policy analyst at the American Civil Liberties Union (ACLU), said attempts by the the UK government to weaken encryption would face many hurdles.

“The trouble is these services are already being used by hundreds of millions of people. I guess you could try to force tech companies to be less secure, but then they would be less secure against attacks for anyone,” he said. “I guess they could ban the iPhone or say you can’t use Google’s services in the UK – but that wouldn’t go down well.”

Soghoian said encryption was used every day by people to pay bills online and make withdrawals from cash machines, and attempts to weaken it would have fundamental consequences. “It suggests that Cameron or the people advising him do not understand technology,” he said, adding that the initiative was likely to fail. “They haven’t even been able to get them to pay their taxes,” he said.