A review of British security procedures has been launched after a hoax caller pretending to be the director of the government's eavesdropping agency was put through to prime minister David Cameron.
Mr Cameron ended the call when it became clear it was a hoax and no sensitive information was disclosed, but the security breach at Number 10 and listening station GCHQ is a major embarrassment.
A warning has been issued to all government departments to be on the alert for further hoax calls.
A first hoax call was made to GCHQ and resulted in the disclosure of a mobile number for director Robert Hannigan.
A second call, purporting to be from Mr Hannigan, was then put through to the prime minister but the conversation is understood to have been “quite brief” before the hoax was exposed.
A government spokeswoman said: “Following two hoax calls to Government departments today, a notice has gone out to all departments to be on the alert for such calls.
“In the first instance, a call was made to GCHQ which resulted in the disclosure of a mobile phone number for the director.
“The mobile number provided is never used for calls involving classified information. In the second instance, a hoax caller claiming to be the GCHQ director was connected to the prime minister.
“The prime minister ended the call when it became clear it was a hoax. In neither instance was sensitive information disclosed.
“Both GCHQ and Number 10 take security seriously and both are currently reviewing procedures following these hoax calls to ensure that the Government learns any lessons from this incident.” – (PA)