David Cameron has revealed new details of his embarrassing call with a hoaxer who was put through to his mobile.
The prime minister emphasised that procedures were being reviewed in light of the mistake, which is just as well given the hoaxer has boasted about being "off his face with booze and cocaine.".
The same prankster also managed to get GCHQ director Robert Hannigan's mobile number, after ringing the spy agency and claiming he could not reach him on his "usual" number and he was needed for a Cobra meeting.
"I've just made complete monkeys out of GCHQ. I've got the mobile number of the director," he told The Sun. "What's more, I am off my face on booze and cocaine."
He added: "I'm definitely going to do it again. It was so easy."
On Monday, Cameron made his audience laugh describing what happened.
He said he was walking in his Oxfordshire constituency, with his daughter Florence on his back, when his Blackberry rang.
"This is the only occasion this has happened to me in this way," he said. "It claimed to be a conference call, which I do very frequently between the director of GCHQ and some of the staff in my office.
"The voice came through, a voice I didn't recognise. The voice said that he was sorry to 'wake me up' which I thought was strange as it was 11 o'clock in the morning.
"I quite rapidly asked 'who is this?' to which the answer came 'it is a hoax call', so I pushed the red button on my Blackberry."
He added: "But every now and again, I suspect these things will happen."
A government spokeswoman said: "Following two hoax calls to government departments, 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."