British prime minister Gordon Brown was caught on tape describing a voter as "bigoted" after she confronted him on the economy and immigration during an election campaign walkabout in northern England.
The comments are a rare gaffe in what has been a tightly scripted and choreographed campaign
Here are some other famed off microphone mistakes
RONALD REAGAN - 1984:
President Ronald Reagan quipped before a radio address to the nation in 1984 at the height of the Cold War. His comments were broadcast live. "My fellow Americans, I'm pleased to tell you today that I've signed legislation that will outlaw Russia forever. We begin bombing in five minutes."
JOHN MAJOR - JULY 1993:
Conservative prime minister John Major called cabinet members opposed to the European Community Maastricht treaty "bastards" in an "off-the-record" chat with a television reporter.
Major, regarded by many as a colourless character dogged by indecision, bantered about his struggle to secure approval of the Maastricht treaty and asked with heavy self-irony: "Why does such a complete wimp like me keep winning?".
DAVID EVANS - MARCH 1997:
In an interview at a local school that he thought was confidential, Conservative member of parliament David Evans said Melanie Johnson, Labour's contender for his constituency, had "never done a proper job" and was the mother of "three bastard children".
Evans, a self-made millionaire, went on to describe John Major as "vindictive and not forgiving" and used the phrase "black bastard" when discussing crime. The transcript of his interview was given to a regional television station.
GEORGE W. BUSH - SEPTEMBER 2000:
Bush did not realise his comments at a campaign stop in Naperville, Illinois, were picked up on the microphone when he leaned over to running mate Dick Cheney and said: "There's Adam Clymer, major-league asshole from the New York Times."
Mr Cheney replied: "Yeah, big time."
Bush later said he regretted everyone heard his comment but sidestepped a question about whether he would apologise to the journalist.