Politicians must always beware of microphones especially during studio interviews, on the off-chance that it may not be switched off. This must rank as one of the basic lessons in politics, forgetting which could lead to all kinds of outcome, some funny, some not so funny.

America's foremost civil rights activist Reverend Jesse Jackson was caught on the wrong foot when he, presuming that the microphone was switched off, let fly at the presumptive Democratic presidential nominee Barack Obama [Images], using crude language to say that he will castrate him over his embrace of faith-based social services.

At the time of the slip-up Rev Jackson was telling another what he thought of Senator Obama's plan to expand US President Bush's federal assistance for faith-based social programmes. Dubbing it as 'talking down to black people', Rev Jackson let fly with the expression. But unfortunately for him, the exchange happened to be near a Fox News microphone that he thought was turned off but which caught every word he said clearly.

The comments were made at Fox News' Midwestern studio, and conservative talk show host Bill O'Reilly promptly aired it on his show.

Realising his gaffe, Rev Jackson sent out a hasty apology to Obama, and held a press conference to describe the senator as 'the culmination of the marches and martyrdom and murder of his own generation's civil rights struggle'.

Jackson's outburst has its origins in Obama's appeal on July 1, in the face of his difficulty in winning over rural and religious voters during his primary, over his faith-based initiative. Jackson had gunned for it, saying white voters could interpret Obama's appeal as a way to avoid government interventions to help African-American communities.

While Obama has not responded to Jackson's comments, his campaign issued a terse statement: 'As someone who grew up without a father in the home, Senator Obama has spoken and written for many years about the issue of parental responsibility, including the importance of fathers participating in their children's lives.'

Obama's spokesperson Bill Burton said: 'He also discusses our responsibility as a society to provide jobs, justice, and opportunity for all. He will continue to speak out about our responsibilities to ourselves and each other, and he of course accepts Reverend Jackson's apology.'

But Jackson's son, Congressman Jesse L Jackson Jr, who is also national co-chair of Obama's campaign, could not be repressed. 'I'm deeply outraged and disappointed in Reverend Jackson's reckless statements about Senator Barack Obama. His divisive and demeaning comments about the presumptive Democratic nominee -- and I believe the next president of the United States -- contradict his inspiring and courageous career,' he wrote.

The divide between the father and son stems from what each sees of Obama's campaign. While Rev Jackson wants Obama to be a more traditional civil rights leader, his son wants the senator to broaden his appeal his appeal among white voters.

Image: Presumptive Democratic presidential nominee Sen Barack Obama (Democrat-Illinois) before the US Capitol. Photograph: Mark Wilson/Getty Images