Spies who abuse their position to access personal information should face a specific criminal offence, an intelligence watchdog has said.
In a long-awaited report on privacy and security, the Intelligence and Security Committee (ISC) reveals MI5, MI6 and GCHQ have disciplined or in some cases dismissed staff for inappropriately accessing personal information obtained through bulk data collection.
However, the Committee said it was concerned to find misuse of GCHQ's interception capabilities is not a specific criminal offence and the law should be changed.
Meanwhile, the Interception of Communications Commissioner revealed details of a " very serious case" last year, in which GCHQ employee deliberately undertook a number of unauthorised searches for related communications data.
The abuse of the systems amounted to gross misconduct and the individual was fired, the Commissioner said.
One member of the ISC, Lord Butler of Brockwell, said there were only "very small single figures of abuse" of surveillance powers by analysts.
The Committee reveals that thousands of communications are read by GCHQ analysts every day, while it calls for a complete overhaul of the laws governing the intelligence agencies.
But human rights and civil liberties groups have hit out at the ISC for lacking independence with Liberty labelling the Committee "a mouthpiece for the spooks".
Shami Chakrabarti, director of rights campaign group Liberty, said: "The ISC has repeatedly shown itself as - so clueless and ineffective that it's only thanks to Edward Snowden that it had the slightest clue of the agencies' antics.
"The Committee calls this report a landmark for 'openness and transparency' - but how do we trust agencies who have acted unlawfully, hacked the world's largest sim card manufacturer and developed technologies capable of collecting our login details and passwords, manipulating our mobile devices and hacking our computers and webcams?"
The Government listening post collect "large numbers of items" they have all been "targeted in some way", the ISC said.
The Committee says it is "unavoidable that some innocent communications may have been incidentally collected" but insists only exchanges involving suspected criminals or national security targets are deliberately selected for examination.
In a heavily-redacted section of the report, largely absent of specific numbers, the Committee says only a tiny percentage of all internet traffic is selected to be read by GCHQ analysts but this still amounts to "around *** thousand items a day".
These are "only the ones considered to be of the highest intelligence value", the ISC adds.
The ISC report says a single law is required to keep in check the powers of the intelligence agencies to snoop on private communications because the current legal framework governing the likes of GCHQ, MI5 and MI6 is "unnecessarily complicated" and "lacks transparency".
However, the Committee found that through the mass surveillance programmes, the intelligence agencies were not attempting to cheat the law.
The ISC inquiry into privacy and security was announced in July 2013 after Mr Snowden, a US intelligence operative, revealed details of bulk interception of private communications by GCHQ and its American counterpart, the National Security Agency (NSA).
Documents handed to newspapers including The Guardian revealed the agencies are able to tap into the internet communications of millions of ordinary citizens through different programmes such as GCHQ's Tempora and the NSA's Prism.
Speaking on behalf of the Committee, Hazel Blears MP said: "There is a legitimate public expectation of openness and transparency in today's society, and the security and intelligence agencies are not exempt from that.
"While we accept that they need to operate in secret if they are to be able to protect us from those who are plotting in secret to harm us, the Government must make every effort to ensure that information is placed in the public domain when it is safe to do so.
"This report is an important first step toward greater transparency.
"Nevertheless, there is more that could and should be done. This is essential to improve public understanding and retain confidence in the vital work of the intelligence and security Agencies."
Rachel Logan, Amnesty UK's Legal Programme Director, said: " The oversight of the security services should be the responsibility of a properly independent body. The Prime Minister holds a veto over who sits on the ISC, what it can examine, and what it can report so there is absolutely no way it can be considered an adequate independent regulator of the activities of our spies."
Open Rights Group e xecutive director Jim Killock said: " The ISC should have apologised to the nation for their failure to inform Parliament about how far GCHQ's powers have grown. This report fails to address any of the key questions apart from the need to reform our out-of-date surveillance laws. This just confirms that the ISC lacks the sufficient independence and expertise to hold the agencies to account."