British Prime Minister Theresa May has suspended Mark Field as a Foreign Office minister while an investigation takes place into an incident in London last night.

Video footage showed Mr Field physically removing climate change protester Janet Barker from a dinner at the Mansion House.

The clip shows Mr Field stopping Ms Barker by pushing her against a column before holding her at the back of the neck and forcefully walking her out of the room.

The incident came as activists interrupted a black-tie event where Chancellor Philip Hammond was giving a speech.

A spokesman for Mrs May said the footage was "very concerning" and he expects a Cabinet Office inquiry into Mr Field's behaviour to take place quickly.

In a statement last night, Mr Field apologised and said he would refer himself to the Cabinet Office over the incident.

Mr Field said he acted out of instinct and was concerned that Ms Barker may have been armed.

In an interview with the BBC, Ms Barker described Mr Field's actions as "over the top".

Asked if she expected resistance, she said: "Yes, but not to the extent which I received.

"I expected to maybe engage in a conversation or two with people, perhaps people blocking my way.

"But certainly not to be grabbed round the neck."

Greenpeace has accused Mr Field of assault and police in the City of London are looking into the incident.

Conservative Party chairman Brandon Lewis said the party will investigate the incident.

Speaking on Good Morning Britain, he confirmed Mr Field had referred himself to the Cabinet Office for investigation and said: "I've spoken to the chief whip this morning and there will be an investigation from our end."

He said it was "very hard to defend" the footage, adding: "It's hard for anybody to look at that and not be astonished at what they have seen."

But he said the investigation would look into the "full details of what happened".

Earlier, conservative MP Peter Bottomley said that Mr Field had done nothing wrong.

He said: "The woman clearly was trying to create a fuss. Most viewers would say it's good that she didn't succeed."

When asked if Mr Field had been heavy-handed with the protester by grabbing her by the back of the neck, Mr Bottomley responded: "No, he reversed her direction and she looked as though she went willingly.

"I think there's no reason to criticise Mark Field ... Of course it wasn't an assault, it was a reversal of direction."

But there was condemnation from other MPs who saw the clip of Mr Field.

Labour MP Jess Phillips said: "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."

Lib Dem MP Chuka Umunna described Mr Field's actions as "totally unacceptable" while 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. But before everyone rushes to instant armchair judgement can I suggest that all of us who weren't there & don't know what was said or done just wait a few hours to hear what those who *were* there say."

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."

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.

A City of London Corporation spokesman said: "We are investigating last night's breach of security at Mansion House and will be reviewing arrangements for future events.

"The protesters were swiftly escorted out of Mansion House by security and the City of London Police."