The Conservatives could win a majority of more than 100 seats in the General Election if the difference in turnout between young and old voters mirrors the 2015 contest, new figures show.
The findings come as time is running out for people to register to vote in the election, with the deadline for applications at 11.59pm on Monday.
New analysis by the Press Association found that Theresa May might enjoy one of the biggest Tory landslides in modern history if people aged 18 to 24 stay away from the polls in similar numbers to 2015, when only around four in 10 voted, compared with more than three-quarters of people aged 55 and above.
The PA's projection of the result, based on the latest opinion polls and using demographic data modelled on the 2015 election, shows the Conservatives on 47% and Labour on 29%, with the Liberal Democrats on 10% and Ukip on 6%.
On a uniform swing across the country, these kinds of vote shares would give the Conservatives a majority close to 120 seats.
But if turnout on June 8 among younger voters rises to the same sort of levels typically seen among the elderly, the projection changes to a Tory majority of 60 to 70 seats.
Even if turnout rose to a notional 100% among all voters aged 18 to 44, the projection still points to a Tory win, however.
The PA's investigation also found that:
:: If turnout at this election was the exact reverse of that in 2015 and was highest among 18 to 24-year-olds, the outcome could be a Conservative majority of 20 to 30 seats.
:: All projections show Ukip winning no constituencies at the General Election, while the Lib Dems could make a net gain of up to four seats.
:: No scenario, based on current opinion polls, produces an outcome where Labour has a majority in the new parliament.
For Jeremy Corbyn to have a chance at becoming prime minister, his party would appear to need a much higher turnout among young people, where Labour support is strongest, plus a general increase in popularity across all age ranges.
Turnout among 18 to 24-year-olds at the 2015 General Election was estimated to be just 43%, compared with 77% of 55 to 64-year-olds and 78% of people aged 65 and over.
This year's election campaign has seen a number of attempts to encourage more young people to vote, including traditional methods, such as publicity campaigns at universities, and online gimmicks, such as a voter-registration themed filter on the photo-messaging service Snapchat.
More than two million applications to vote have been made since the snap election was announced, although not all of these will be new applicants or people who are eligible to vote.
Anyone who is not registered to vote has until midnight to apply online at gov.uk/register-to-vote.
The Electoral Commission told the Press Association: "With the registration deadline in sight, the commission is advising everyone who has not yet registered to do so as soon as possible to ensure that they can have their say on 8 June."
For more information, visit electoralcommission.org.uk.
:: The PA's analysis is based on all polls published during the past four weeks by ComRes, ICM, Ipsos-MORI, Opinium, and YouGov. It uses estimates of the size of the electorate and the population from the Electoral Commission and the Office for National Statistics.