EXCLUSIVE: Spooks and serious crime investigators now need permission from Home Secretary and High C

DOUBLE LOCK: A secretary of state and now High Court judge have to agree the snooping

THE security services will now have to jump through an extra hoop to be able to eavesdrop on suspected terrorists' and organised criminals' phone calls and access electronic communications.

Intelligence agencies MI5, MI6 and GCHQ plus the National Crime Agency (NCA), Met Police and other agencies allowed to snoop in certain circumstances on serious terror or gangland suspects now need two forms of clearance after legislation changes came into force.

Major terror plots on UK soil and international crime gangs have been foiled by investigators listening in to live phone calls made by suspects or accessing their emails and electronic messaging systems, even though the intelligence cannot be used to prosecute in court.

Live phone intercepts, as they are known, are done from specialist centres, including at the

UK FBI: Live phone intercepts take place at the NCA HQ in Vauxhall

NCA headquarters in Vauxhall, south London, with listeners making notes of the conversation being secretly listened to.

Previously agencies wishing to use the power, governed by the Regulation of Investigatory Powers Act 2000, had to first seek approval from a secretary of state, before snooping could begin.

Now, following a number of human rights challenges to the use of the powers, a new "double lock" system is in force for the power which can only be used to detect serious crime or threats to national security.

Investigators still need the Government approval as before, but once that is given, it then goes before the new Investigatory Powers Commissioner’s Office, where it is reviewed by a High Court judge, who also has to approve the use on each occasion.

Three other agencies, HMRC, the Police Service of Northern Ireland and Police Scotland are allowed to use the power.

HQ: The GCHQ headquarters in Cheltenham as seen from above

A GCHQ spokesman said: "With the Investigatory Powers Act (IPA) a ‘double lock’ system was introduced which requires warrants for the use of these powers to be authorised by a Secretary of State and approved by a senior High Court judge.

"An Investigatory Powers Commissioner has also been created to ensure robust independent oversight of how these powers are used."

An HMRC spokesman added: "All intercepting agencies have to meet a number of tests before a warrant can be sought.

"In HMRC’s case the investigation must relate to the prevention and detection of serious crime - these will be cases involving organised criminal attacks on the tax system involving many millions in revenue."