There is very little else that could justify this and anyone can see that this could have been done without physical contact.
Foreign Office minister Mark Field should be sacked after video footage showed him physically removing a climate change protester from a dinner at Mansion House, a Labour shadow cabinet MP has said.
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The video clip shows Mr Field stopping a female protester by pushing her against a column before holding her at the back of the neck and forcefully walking her out of the room.
It came as activists interrupted a black-tie event where Chancellor Philip Hammond was giving a speech. According to ITV, Mr Field has referred himself to the Cabinet Office for investigation and has apologised "unreservedly" to the protester.
In a statement to the broadcaster, he is quoted as saying: "In the confusion many guests understandably felt threatened and when one protester rushed past me towards the top table I instinctively reacted.
"There was no security present and I was for a split-second genuinely worried she might have been armed. As a result I grasped the intruder firmly in order to remove her from the room as swiftly as possible."He added that he "deeply" regretted the incident and would cooperate fully with a Cabinet Office investigation.
After the footage was released Labour MP Jess Phillips tweeted: "She posed no credible threat from what I can see. There is very little else that could justify this and anyone can see that this could have been done without physical contact.
"Every MP has to deal with protest and conflict, it is done with words. To watch this is so so awful."
Fellow Labour MP Dawn Butler said it was "horrific" and called for Mr Field to be sacked or at least suspended.
Ms Butler, who is shadow secretary of state for women and equalities, tweeted: "Conservative Foreign Office Minister Mark Field violently grabs a woman as she protests about climate change at the bankers' banquet. This appears to be assault. He must be immediately suspended or sacked. Due to Violence against women.
"I'm sure I'm not the only one who is wondering why no one intervened. So much violence does not seem justified. An investigation needs to take place as soon as possible."
Independent MP Sarah Wollaston said it was "Absolutely shameful, a male MP marching a woman out of a room by her neck."
Tory MP George Freeman tweeted: "This looks appallingly rough handling of a woman climate protester in a dress."
Conservative former Middle East minister Alistair Burt was shown the clip on BBC's Newsnight. He said: "I've no appreciation of the context... Mark will answer for himself but it looks to be a very difficult situation for everyone concerned."
When contacted by the Press Association, Foreign Secretary Jeremy Hunt, who is Mr Field's boss, responded with a text saying "sorry can't talk now".
Mr Hammond had barely started his address when activists interrupted the event in the City of London on Thursday night. The disruption lasted several minutes before a slow hand clap broke out among the seated guests, and Mr Hammond got back to his feet at 9.05pm.
To a round of applause, Mr Hammond then said: "The irony of course is that this is the Government that has just led the world by committing to a zero-carbon economy by 2050."
Greenpeace later said 40 of its activists, some of whom wore red evening dresses with sashes that read "climate emergency", had interrupted the event, which was being broadcast live on television.
Footage later released by Greenpeace shows a line-up of protesters, including men who are wearing black suits and bow ties and women in red dresses and sashes, walking alongside the building, then rushing up a set of stairs and streaming into the dining hall.
A spokesman said he would not comment on how the group managed to evade security to get into the high-profile event.
In response to the video of Mr Field, the organisation tweeted: "Instead of assaulting peaceful women protesters, @MarkFieldUK would be better off spending his time tackling the #ClimateEmergency."
Greenpeace said the activists had wanted to deliver a speech on how the current system has failed. Mr Hammond paused his speech at the request of an official in the dining hall who asked him to let security and other staff clear the noisy activists away.
The sound of alarms could be heard in the background. Senior captains of industry and top City executives were among the invited guests.
Retiring Bank of England Governor Mark Carney later made his final Mansion House speech, which was about the future of finance. He spoke about a new economy driven by changes in technology, demographics and the environment.
A City of London Police spokesman said: "We were alerted at 9.03pm. Officers arrived to help with their ejection. Once in the presence of the police, the protesters were co-operative and left the premises. No arrests were made."
Brendan Montague is editor of The Ecologist. Helen William and Jennifer McKiernan are reporters for the Press Association.