Greenpeace accused British minister Mark Field of assault after the Conservative politician was filmed physically removing a climate change protester from a dinner in the City of London.
Field accosted the female activist as she walked towards finance minister Phillip Hammond, pushing her against a column at Mansion House before holding her by the neck and frogmarching her out of the room.
Greenpeace activist Areeba Hamid said she was "shocked at the footage of an elected MP and government minister assaulting one of our peaceful protesters."
Field told ITV that he "deeply" regretted his actions, saying that "in the confusion many guests understandably felt threatened and when one protester rushed past me towards the top table.
"There was no security present and I was for a split-second genuinely worried she might have been armed."
The junior Foreign Office minister has referred himself to the Cabinet Office for investigation.
Labour MP Jess Phillips called the footage "so, so awful" while fellow Labour MP Dawn Butler said it was "horrific" and called for Field to be sacked or suspended.
But Tory MP Peter Bottomley argued that "the woman clearly was trying to create a fuss" and that "most viewers would say it's good that she didn't succeed."
Greenpeace later said 40 of its activists had interrupted the event.
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