The Downing Street blunder followed a prank call to the spy agency itself, which saw a mobile phone number disclosed for its director, Robert Hannigan. It's not yet clear whether the same individual is behind both incidents, and Cameron is said to have ended the call when the joke became obvious.
When the man talked to The Sun about his actions, he said he was "off my face on booze and cocaine". He also explained to the paper: "I've just made complete monkeys out of GCHQ. I've got the mobile number of the director. I'm definitely going to do it again. It was so easy".
Although no secret material was given out during the call to the prime minister, it's a pretty notable security breach for his office. The BBC says Downing Street is going to review its security procedures and GCHQ is also examining what happened. The GCHQ director's number that was given out is said to be an "unclassified phone" and not a secure line for sensitive information.
A government spokesperson reports that a notice has been given out to departments to be wary of more hoax calls and stressed that no sensitive information was revealed as a result of Cameron's conversation with the man. the spokesperson added: "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."