Home secretary Amber Rudd has called end-to-end encryption on messaging services such as WhatsApp and iMessage "completely unacceptable" in the wake of the terrorist attack on Parliament.
"There should be no place for terrorists to hide," she said, speaking on the BBC's Andrew Marr Show, responding to reports that the attacker Khalid Masood used the Facebook owned app minutes before the attack.
"We need to make sure that organisations like WhatsApp, and there are plenty of others like that, don't provide a secret place for terrorist to communicate with each other."
She continued: "It used to be that people would steam open envelopes or just listen in on phones when they wanted to find out what people are doing - legally through warrantry - but on this situation we need to make sure that our intelligence services have the ability to get into situations like encrypted WhatsApp."
She said that the access to end-to-end encrypted messages was something "completely different" to Apple's refusal to give the FBI "backdoor" access to the iPhone of an attacker.
"We're not saying open up, we don't want to go into the cloud, we don't want to do all sorts of things like that. But we do want them to recognise that they have a responsibility to engage with government, engage with law enforcement agencies when there is a terrorist situation. We would do it all through the carefully thought through, legally covered arrangements," she said.
"They cannot get away with saying 'we are a different situation' - they are not."
Amber Rudd's message to Tim Cook
She said she would ask Apple boss Tim Cook to think again "about other ways of finding out, helping us work out, how we can get into the situations, like WhatsApp on the Apple phone".
"It's not necessarily Apple itself, sometimes its WhatsApp or the other situations on it. Which is why I'm calling in a lot of the organisations who are relevant to that this week to ask them to work with us to deliver the answer. It's not about them standing back from us, this is a national problem," she said.
Rudd expressed confidence that she would be able to get the tech companies on side without legislation and is meeting with many of them this week. And she will propose the creation of an industry-wide board to self-regulate.
"I'm not saying I want to get into your WhatsApp, what I'm saying is where there are situations where there are ongoing investigations with terrorists. Those people have families and children, they should be on our side and I'm going to try and win that argument." she said.
She also warned tech companies such as Google, Facebook and Twitter that they are now publishing companies and that the government would not hesitate at pursuing legislation when it comes to extremist content on their sites.
"What these companies have to realise is that they are now publishing companies they are not technology companies, they are platforms and we need to make sure that that stops.
"The best people who understand the technology, who understand the necessary hashtags, to stop this stuff even being put up - not just taking it down, but getting up in the first place - are going to be them. That's why I'd like to have an industry-wide board set up where they do it themselves They could do this, I want to make sure they do."
It comes after a week of mounting pressure on Google, by advertisers who have pulled their spending on YouTube since it was found that they were appearing next to extremist content.
Cook and others in the technology industry have warned that there is no way to give authorities access to encrypted devices or messages without creating a so-called backdoor vulnerable to hackers and others increasing security risks to users.
Tim Cook last year said access to information on an encrypted iPhone was something "we simply do not have, and something we consider too dangerous to create".
He was supported by other top tech bosses such as Twitter's Jack Dorsey, Facebook's Mark Zuckerberg and Google's Sundar Pichai.
“I’ve seen this after every terrorist attack,” said Jamie Bartlett from the Centre for the Analysis of Social Media at Demos and the University of Sussex.
“The problem now is everything is encrypted and people rely on it and most people find it valuable. Without encryption, the police would be inundated with calls about cybercrime. Encryption is also brilliant for the Home Office - the anti-terrorism team will be frustrated they don’t have access but the cybercrime team will welcome it. Even GCHQ is telling business to be encrypted,” he told City A.M..
“This stuff [products and services] is designed to intentionally not have access. Often they are designed so that you can't have a backdoor. Companies know that others will try and get in. It would undermine the security of the whole system,” he added. But the problem is unlikely to go away.
“This [a ban on encryption] would be a short term solution. The rise of these apps will continue. We need a different approach and sometimes that means accepting that they [authorities] won’t be able to access it and we can’t get all the information we would like,” he said.
Bartlett also noted that the tech companies in Rudd’s firing line have vastly improved their engagement with governments, responding more quickly and with more relevant information compared to four years ago. And he also warned of the risk of pushing people onto other less respected services that offered encryption and that are less likely to engage in this way with authorities.
Dan Korski, a former government special advisor, said: "Undermining the integrity of products like Whatsapp could also create unintended consequences for industries that rely on various forms of security communication - like banks, charities, insurance companies and retailers."
"The message that a hardline position on encryption sends to innovators and businesses about Britain is a problematic one. Like it or not, the digital workforce is highly mobile and prioritises economies that are seen to be technology friendly. So do companies. The UK has benefited from being seen as tech-friendly and pro-innovation. The government may be willing to accept the consequences of its message in an effort to strengthen law enforcement but it could in the final instance mean a smaller digital economy, fewer jobs and the end of various applications and services in the UK.
"The best strategy is therefore not the megaphone but quiet dialogue especially with smaller companies who don't even understand the challenges on their networks; and a greater investment in more traditional, human-focused intelligence and operations."
The former Met deputy assistant commissioner and Lib Dem shadow home secretary Brian Paddick labelled Rudd's plans draconian and ineffective.
"These terrorists want to destroy our freedoms and undermine our democratic society. By implementing draconian laws that limit our civil liberties, we would playing into their hands," he said.
"My understanding is there are ways security services could view the content of suspected terrorists' encrypted messages and establish who they are communicating with. Having the power to read everyone's text messages is neither a proportionate nor an effective response. The real question is, could lives have been saved in London last week if end-to-end encryption had been banned? All the evidence suggests that the answer is no."
Read more reaction from experts in technology, policy, intelligence and security, here.