The BBC's political editor Nick Robinson said he was "not remotely ashamed" after being filmed stamping on an anti-war protester's sign.
A film clip posted on the website of the New Statesman magazine showed him grabbing the sign which was being waved behind him while he was broadcasting from Westminster yesterday.
He is shown trying to pull the sign, which reads "Cut the war not the poor", apart before stamping on it while a protester shouts: "You should be ashamed of yourself, mate. You should be ashamed."
Confronted after the incident, Robinson told a protester: "I'm not remotely ashamed of myself. Why should I be ashamed of myself?"
Robinson, who has been political editor at the BBC since 2005, is not the first broadcaster to lose their temper within sight of Westminster recently.
The political editor of Sky News, Adam Boulton, was involved in an on-air spat with Labour's former head of communications Alastair Campbell shortly after the general election.
He accused Mr Campbell of "casting aspersions" and trying to tell him what to think during the fiery exchange.
His colleague Kay Burley was heckled by a protester chanting "Sack Kay Burley, watch the BBC" while she carried out a live interview - also in Westminster.
Writing on his blog, Robinson said he regretted losing his temper.
He wrote: "If you were watching the 6 O'Clock News last night, you may have seen a Troops Out sign on a large pole being waved behind my head. I have a confession. After the news was over, I grabbed the sign and ripped it up - apparently you can watch video of my sign rage in full glorious technicolour on the web. I lost my temper and I regret that.
"However, as I explained afterwards to the protesters who disrupted my broadcast, there are many opportunities to debate whether the troops should be out of Afghanistan without the need to stick a sign on a long pole and wave it in front of a camera.
"I am a great believer in free speech but I also care passionately about being able to do my job reporting and analysing one of the most important political stories for years."