(CNN) - UK Prime Minister Theresa May has suspended senior politician Mark Field from office after video emerged of him grabbing and manhandling a protester at an event in London on Thursday evening.
"The Prime Minister has seen the footage and found it very concerning. The police have said they are looking into reports over this matter and Mark Field has also referred himself to both the Cabinet Office and Conservative Party," the Prime Minister's spokesperson told CNN.
"He will be suspended as minister while the investigation takes place," the spokesperson added.
The Conservative Party lawmaker was at a black tie event at the Mansion House on Thursday when protesters from Greenpeace UK, dressed in red and wearing sashes with the words "climate emergency," interrupted a speech by the UK Chancellor, Philip Hammond.
During the protest, footage shows, one woman walked past where Field was sitting, at which he got up from his seat and grabbed her around the neck, pushing her against a nearby pillar. After a brief scuffle, Field is seen leading the woman out of the room by the back of her neck.
According to CNN affiliate ITV News, Field has apologized for grabbing a protester by the neck, saying he "instinctively reacted" after guests felt threatened by the woman, who was acting peacefully at the time and was not armed.
"There was no security present and I was for a split-second genuinely worried she might have been armed," Field, who is Member of Parliament for Cities of London and Westminster and a minister in the Foreign Office, said in a statement to ITV.
"As a result I grasped the intruder firmly in order to remove her from the room as swiftly as possible. I deeply regret this episode and unreservedly apologize to the lady concerned for grabbing her, but in the current climate I felt the need to act decisively to close down the threat to the safety of those present."
Field said he had referred himself for investigation to the Cabinet Office, as numerous opposition lawmakers called for his immediate sacking or resignation.
A City of London Police spokesman said they were called to the Mansion House after protesters refused to leave.
"Officers arrived to help with their ejection. Once in the presence of the police, the protesters were co-operative and left the premises," he said. "No arrests were made."
The Prime Minister's spokesperson said the Mansion House has said it is "looking into the breach of security that took place," adding: "We believe that it's right that they are reviewing security arrangements."
Opposition lawmakers were quick to demand Field's resignation after the video emerged late Thursday.
"This is horrific," Labour Party lawmaker Dawn Butler wrote on Twitter. "Conservative Foreign Office Minister Mark Field violently grabs a woman as she protests about climate change at the bankers' banquet."
Butler said Field appeared to have committed "assault" and "must be immediately suspended or sacked."
Another Labour lawmaker, Tonia Antoniazzi, said Field "should resign and be arrested. I don't care in what order."
"No one who reacts like this to a peaceful protest should be sitting in our parliament," she added.
Field works in the Foreign Office under Secretary of State for Foreign and Commonwealth Affairs Jeremy Hunt, who on Thursday was declared one of the final two candidates, alongside Boris Johnson, to be the next Conservative Party leader and therefore British Prime Minister.
The incident comes amid heightened environmental activism in the UK, amid frustration that the Conservative government is not doing enough to tackle the climate emergency.
In a statement on Thursday's protest, Greenpeace UK campaigner Areeba Hamid said that "business as usual is no longer an option."
"The real bottom line, the priority that needs to come before all others, is not profit, revenue or growth, but survival. That needs to be recognized in every boardroom and on every balance sheet, starting with the Chancellor's," she said.
"The people in this room have been funding climate change, and we're not giving the banks and hedge funds a pass for their unethical investment decisions anymore ... The serious, sensible, grey-suited grown-ups in the room ignored the warning signs and crashed the economy in 2008. We can't afford to let them crash the climate too."
Young people in particular have taken up the fight for greater climate action, with students staging walkouts and joining the Extinction Rebellion protests.
On Twitter, ITV News political correspondent Paul Brand wrote "if ever there was an image that sums up the Conservative Party's disconnect with the younger generation right now it's a man in black tie at an elite dinner grabbing a climate change protestor by her neck."
CNN's Warda Al-Jawahiry contributed to this report.
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