Some 74% of people who were too young to cast a ballot in the 2016 Brexit referendum but have since reached voting age would back remain if a second public vote were called, according to a new poll.

The proportion of the new voters – an estimated 2 million young people – supporting remain rises to 87% among those who say they would “definitely” take part in the referendum.

The survey, carried out by BMG on behalf of the anti-Brexit youth groups Our Future, Our Choice and For Our Future’s Sake, suggests the youth vote would be crucial in any second remain campaign and could significantly boost its chances of overturning the 2016 leave result.

The survey polled two groups: those who were too young to vote in 2016 and those who were eligible to vote but chose not to. Some 72% of those too young to vote in the original referendum feel it would be unfair if Britain left the EU without them having been able to vote on the issue.

Only 3% of this demographic believe Britain’s standing in the world has increased since the referendum in June 2016.

Further figures from the survey reveal that only 4% of this age group have had contact with their local MPs regarding Brexit.

The proportion of young voters who would be angry if Britain left the EU without a public vote significantly outweighs those who would be happy – 55% to 9%.

Young people are rightly furious, watching older generations take our futures away from us Kira Lewis, activist

Lara Spirit, co-founder of Our Future, Our Choice, said: “It’s great that we were able to poll a group that isn’t talked about enough in the Brexit debate – those who didn’t get a vote because they were too young.

“The government hasn’t done anything to address young people’s concerns around Brexit. That’s why we’re more united on the issue than on anything else.”

Kira Lewis, speaking on behalf of For Our Future’s Sake, said: “Young people are rightly furious, watching older generations take our futures away from us. We will be marching on 23 March to demand a people’s vote.”

Separately, constituency-by-constituency analysis by YouGov of more than 25,000 voters shows that in only two out of 632 constituencies do a majority of voters want their MP to back Theresa May’s Brexit deal.

Commenting, Peter Kellner, a past president of YouGov, stated: “The coalition that produced a narrow majority for Brexit three years ago is falling apart. It brought together traditionalists in Conservative Britain who saw the EU as a threat to British values and sovereignty, with families in Labour’s heartlands who felt that ‘Brussels’ threatened their living standards and their children’s job prospects.

“The prime minister’s plan is unpopular essentially because few people in either group think it tackles the threat they face. The fact that only two constituencies in the entire country – not including her own – want their MP to support her deal shows just how risky it would be for the prime minister to force this deal on the people now.”

• This article was amended on 10 March 2019. An earlier version wrongly stated that the poll had shown that 87% of young people who have become eligible to vote since the 2016 referendum would vote in a second referendum. This has been corrected.