UK spy boss Charles Farr said that the services are classified as external communications and the spooks can hack into your account without needing a warrant.
The news came out as part of a continuing legal battle with campaign group Privacy International (PI).
Charles Farr, director general of the Office of Security and Counter-Terrorism, told PI that Facebook, Twitter, YouTube and web searches on Google, webmail services such as Hotmail and Yahoo, are classified as "external communications", which means that they can be intercepted without the need for additional legal clearance.
If you have webmail or social networking accounts in the EU the government would need a search warrant signed by a minister and that can only be issued when there is suspicion of illegal activity.
However if your accounts or searches are on Google or your posts on Facebook they are sending information overseas which can be collected under a broader warrant which does not need to be signed by a minister.
Farr said point out that data collected in this way "cannot be read, looked at or listened to" except in strictly limited circumstances.
Apparently there is a “significant distinction" between intercepting material and a person actually reading, looking at or listening it.
James Welch, legal director of human rights group Liberty, told the BBC that the security services consider that they're entitled to read, listen and analyse all our communications on Facebook, Google and other US based platforms.
Eric King, deputy director of Privacy International said the revelation showed that spy agencies operated under their own laws and cannot be considered accountable to parliament and to the public they serve when their actions are obfuscated through secret interpretations of Byzantine laws.