Any social media – Twitter, Facebook posts or YouTube postings – are legal targets for mass online surveillance, Charles Farr, director general of the Office for Security and Counter Terrorism at the Home Office, argues. This is hardly surprising.

What Farr's analysis of the legal status of online surveillance also reveals is the government's belief that documents and direct messages on Twitter and Facebook are also legal targets, which can be monitored without a warrant, if they are hosted outside the UK.

Thus virtually anything involving Google's servers, none of which is in the UK, is "external communication".

Farr's 48 page, 162 paragraph statement was made in response to the case brought by Privacy International with Amnesty International against the UK government before the Regulation of Investigatory Powers Tribunal (which is meant to oversee how well the government follows Ripa, its own Regulation of Investigatory Powers Act).

It is a detailed document which invokes a lot of dancing around the subject. For instance, he will neither confirm nor deny the authenticity of the Edward Snowden documents which formed the basis of the Guardian's story on Tempora, the cable tapping operation that has led to this case. This creates the conflicting situation of one part of the government insisting that the documents' carriage poses a serious security threat, while Farr is insisting that it has "not accepted the provenance" of the same documents.

The document explains how, in the eyes of the government, even our searches of Google and YouTube are fair game for monitoring. As Farr explains, a Google search "is a communication between the searcher's computer and Google's web server" and, as he points out, "its largest centres are in the US, and its largest European centres are outside the British Islands". Hence, he says, searching on Google or its video subsidiary YouTube falls under "external communications", and so doesn't trouble Ripa.

Similarly with Facebook private messages, and though it isn't explicitly mentioned Twitter direct messages, both of which you would normally expect to be private. If either side isn't in the UK, then it can be tapped via Tempora.

The reaction of Google and Facebook to Farr's statement has been brisk. A Google spokesperson said: "We disclose user data to governments in accordance with the law, and we review all such requests carefully. Google has not joined any program that would create a 'back door' for government to access private user data." The spokesperson also reiterated Google's point that "government does not have access to Google's servers".

Facebook declined to comment, though sources close to the company suggested that enhanced encryption now being deployed should make it increasingly difficult for governments, whether in the US, UK or elsewhere, to tap into private discussions.

Farr, however, is unrepentant: "The only practical way in which the government can ensure that it is able to obtain at least a fraction of the type of communication in which it is interested is to provide for the interception of a large volume of communications," he writes. And as he sets out, many of those might be messages you thought were private.