The turnout among young people aged 18 to 24 in the EU referendum was almost double the level that has been widely reported since polling day, according to evidence compiled at the London School of Economics.

The new findings – based on detailed polling conducted since the referendum by Opinium, and analysed by Michael Bruter, professor of political science and European politics at the LSE, and his colleague, Dr Sarah Harrison – suggests the turnout was 64% among this age group.

It has been widely assumed since the referendum that the turnout among young people was around 36% – a figure that has allowed Brexit campaigners to say young people cannot claim that they were betrayed by older pro-Brexit voters, as almost two-thirds did not bother to vote.

Bruter and Harrison say the lower and wrong estimate was based on information released by Sky Data which relied on data compiled after last year’s general election, which looked at the proportion within each generation who said they always vote.

The new, far higher, figures emerged after Opinium conducted post-referendum polling among 2,002 people that asked four questions about how and whether they voted. They asked whether people voted at polling stations or by post, whether they were registered but did not vote, and whether they were not registered at all.

The results found that 64% of those young people who were registered did vote, rising to 65% among 25-to-39-year-olds and 66% among those aged between 40 and 54. It increased to 74% among the 55-to-64 age group and 90% for those aged 65 and over. It is thought that more than 70% of young voters chose to remain in the EU.

In a report, Bruter and Harrison say: “The question of whether young people voted or not is politically important for two critical reasons. First, because there continues to be a significant proportion of younger voters who say that they are unhappy with the result of the referendum and want to be heard, and one of the key arguments that has been made in answer to them is that they should have bothered to vote if they cared that much. And, second, because the government chose not to give the right to vote to 16- and 17-year-olds in the referendum. It is fair to ask whether allowing them to vote could have changed the result of the referendum or not.”

They say the assumption that a majority of young people who were registered did not bother to vote can be laid to rest. “While young people voted a little bit less than average, they were probably quite close to the national average (only 8% below according to our survey).”

Bruter added that if 16- and 17-year-olds had been allowed to vote, the result would almost certainly have been closer, reducing the ability of the Leave camp to claim a clear victory.

“Allowing 16-to-17-year-olds a vote would have added nearly 1.6 million potential citizens to the electorate, but it is of course extraordinarily difficult to know if it might have affected the outcome of the referendum. On balance, the results of our surveys on the turnout of 18-to-24-year-olds would suggest that it would not have been enough to overturn the result of the referendum … but it would have almost certainly reduced the advantage of Leave to such a point (likely less than 500,000 votes) that the very concept of a majority would have been highly controversial.”