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 for all the main political parties ahead of May 6 elections.
Here are some other famed off microphone mistakes
* RONALD REAGAN - 1984:
-- U.S. 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 Prime Minister John Major as "vindictive and not forgiving." 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."
-- The Republican nominee later said he regretted everyone heard his comment but sidestepped a question about whether he would apologise to the journalist.
* GEORGE W. BUSH - 2006:
-- Bush's candid remark to Prime Minister Tony Blair was picked up by an open microphone during the closing lunch at the G8 summit in Russia.
-- In the remarks, he expressed his frustration with the United Nations, Hezbollah's attacks on Israel and the group's backers in Syria.
-- "See, the irony is that what they need to do is get Syria to get Hezbollah to stop doing this s---, and it's over," Bush told Blair as he chewed on a buttered roll.
* GORDON BROWN - APRIL 2010
-- "That was a disaster," Brown was heard saying as he got into a car after speaking to a vote, still wearing a broadcast microphone. "Whose idea was that? It's ridiculous."
-- When asked what the voter had said, Brown said: "Everything, she's just sort of a bigoted woman."
(Writing by David Cutler, London Editorial Reference Unit)