British officials say they are reviewing security measures in the government after a hoax caller managed to get through to Prime Minister David Cameron on the phone.

Downing Street officials say the caller, who claimed to be the director of the eavesdropping agency GCHQ, Robert Hannigan, was put through to Cameron on Sunday. They said Cameron ended the call when it became clear it was a hoax, and no sensitive information was disclosed.

Officials said earlier in the day, a caller obtained Hannigan's cell phone number by phoning GCHQ.

All government departments have been alerted for similar calls and security procedures are being reviewed.