Field apologized for grabbing the woman by the neck at a black-tie event, saying he reacted "instinctively". But said he was worried she may have been armed, the BBC reported.
The Conservative Party lawmaker had been in attendance at the event at Mansion House on Thursday where Chancellor Philip Hammond was giving a speech. Soon, protesters from Greenpeace UK, dressed in red wearing sashes with the words "climate emergency" interrupted it.
During the protest, video showed, 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 was seen leading the woman out of the room by the back of her neck.
Field said he had referred himself to the Cabinet office for an investigation as numerous opposition lawmakers called for his immediate sacking or resignation.
The City of London Police said: "We have had a number of third-party reports of a possible assault. These are being looked into."
Greenpeace climate campaigner Areeba Hamid told the BBC the activist was "in shock", but was recovering and had been reassured by the "outpouring of support" online.
Labour Party's Shadow Women and Equalities Minister Dawn Butler was among those who criticized Field, tweeting: "This is horrific... He must immediately be suspended or sacked."
Fellow Labour MP Tonia Antoniazzi added: "No one who reacts like this to a peaceful protest should be sitting in our Parliament."
Meanwhile, Liberal Democrat MP Chuka Umunna described Field's actions as "totally unacceptable", while former Tory MP Sarah Wollaston said it was "absolutely shameful, a male MP marching a woman out of a room by her neck".
One of Field's Conservative colleague, MP Peter Bottomley, said he had done nothing wrong.
( With inputs from IANS )