This is how the case for mass surveillance is being made in the UK.

Facebook is used by millions in the UK, but they paid not a single penny in UK tax in 2012.

First, a cheap shot. Does the UK expect every website in the world that their citizens use to pay them taxes?!

Even worse, they refuse to recognise UK legislation requiring them to provide our agencies with the content of communications on their networks when served with a UK interception warrant.

Then, a lie. Of course Facebook responds to UK intercept warrants.

The problem that this story is complaining about is the fact that Facebook doesn't perform mass monitoring of the content of private communications between users and report those conversations to the authorities.

As we have seen with the killers of Lee Rigby, this stance can have disastrous consequences.

Apparently the killers of Lee Rigby discussed their extremism in private conversations on Facebook.

Facebook and the other providers like to defend their non-compliance with excuses about the need to protect privacy and maintain the rights of their users. But this kind of pseudo-libertarianism is profoundly unconvincing.

After all, in cases of child pornography and exploitation, these internet companies are only too willing to pass on information to law enforcement authorities. So why is the same logic not applied to terrorist activities, where innocent lives are also at stake?

Indeed Mark Field MP, a member of the Commons Intelligence and Security Committee, has rightly said this week that ‘if Adebowale had been preparing a paedophile attack, not a terrorist one, the authorities would have been alerted’.

Internet companies like Google and Facebook monitor the content of private communications for file transfers, and they check the hashes of those files against a list of known child porn images for matches. This practice is defended based on its narrowness, but it raises a variety of concerns, and you're looking at one of them. Once you pierce the veil of private conversations and start reporting their content to the government, you open up a slippery slope that many people are eager to slide down. If Google and Facebook monitor private conversations for this one thing, then people might ask why they don't monitor those conversations for other things. General searches of language that seems extremist is much more broad than file hash comparisons for known child pornography, and much more prone to false positives and misinterpretations.

If Facebook and Google are shamed into complying with this kind of demand, they will have to set up an infrastructure for sifting through everyone's private conversations and flagging discussions for police based on their content. Once that system is established, there is no limit to the purposes for which it might be put. This will be the end of the sanctity of private communications.

Reading between the lines of the UK leadership's call for mass surveillance.