The UK's intelligence services can monitor citizens' social media, search engine and YouTube visits because these are "external communications" that don't require a specific warrant, the government has argued in a legal submission made public by campaign group Privacy International.
As it stands, the internet communications of a UK resident, such as social media and emai,l can only be intercepted on an 'intrusive' way under section 8(1) of the Regulation of Investigative Powers Act (RIPA) 2000 using a warrant mentioning a person's name and address obtained from the Home or Foreign Secretaries.
However, RIPA also allows more indiscriminate self-authorised warrants in certain circumstances which the detailed 48-page legal submission from Office for Security and Counter-Terrorism director general Charles Farr now reveals include that communications are deemed to be 'external' to the UK.
Exactly what 'external' means in the context of the internet is complex but the principle explained in the submission is that the servers or services used to host them should be physically outside the UK.
"By defining the use of 'platforms' such as Facebook, Twitter and Google as 'external communications', British residents are being deprived of the essential safeguards that would otherwise be applied to their communications - simply because they are using services that are based outside the UK," argued Privacy International, summing up the implications of this definition.
What this means is that an email sent via Google can't be monitored if it is sent and received within the UK even if a foreign server transmits the data. However, because Facebook, Twitter and search engines are platforms that host their services externally, monitoring of these would be allowed.
"The security services consider that they're entitled to read, listen and analyse all our communications on Facebook, Google and other US-based platforms," commented James Welch, legal director of Liberty, one of the coaltion of groups that have mounted a legal challenge to GCHQ's alleged monitoring using the Tempora system revealed last summer by Edward Snowden.
"If there was any remaining doubt that our snooping laws need a radical overhaul there can be no longer. The agencies now operate in a legal and ethical vacuum; why the deafening silence from our elected representatives?"
There are several complex issues at work in this but the government's definition of 'external' is shaky in relation to some of the services mentioned by Farr.
According to Farr, a Google search or a request to watch a YouTube video can be classed as 'external' if the servers hosting the service are outside the UK, which in most cases they will be.
But a search or video stream are also technically returned to the user inside the UK which makes them analogous to an email sent from the UK, routed through a foreign server and then returned to a second UK recipient. And yet it appears that one of these, the email, is deemed subject to a warrant while search and YouTube data can be spied on with few restrictions.
This wouldn't apply to Twitter or Facebook because that is a foreign-based platform that distributes messages to more or less anyone willing to read them from any location in the world. The data is not, conceptually at least, making a return 'internal' journey to a specific recipient.
The government position as argued by Farr is that this doesn't constitute mass unwarranted surveillance and that security staff are aware of the legal limits on their powers.
Whether the security services are exploiting an ambiguity or not, the mechanisms through which the security services gain access to internet traffic remain controversial. In 2013, Privacy International lodged a complaint with the OECD alleging that telecoms firms were secretly collaborating with GCHQ in tapping their fibre optic cables.