The elections watchdog has raised concerns about "troubling" claims that some electors cast more than one vote at the general election as it released figures showing the electorate has reached record levels.
Nearly two million young people applied to vote after Theresa May announced she planned to call a snap election, according to the Electoral Commission.
Around 500,000 more people were registered for the June 8 poll than at the 2015 general election, taking the electorate to 46.8 million, the largest so far, it said.
But the watchdog called for urgent action to tackle the number of duplicate applications by people unaware they are already registered, which puts the system under strain by increasing the number of checks officials need to carry out.
The Electoral Commission also called for the Government to consider ways of cutting the risk of abuse of voting rules.
Although some people, such as students, are allowed to be registered in two areas, it is illegal to vote more than once in a general election.
The watchdog said it had not found evidence of widespread abuse but had received more than 1,000 emails from members of the public, along with 38 letters from MPs, raising the issue and it is working with police on how to investigate allegations.
Its report states: "Although people may lawfully be registered to vote in more than one place in certain circumstances, it is troubling that some voters appear to have admitted voting more than once at the general election, which is an offence."
An increase in the number of younger voters is claimed to have fuelled the surge in support for Jeremy Corbyn's Labour Party.
Overall, 2.9 million people tried to register to vote, with 96% applying online and 69%, 1.9 million, of those aged under 34.
But electoral registration officers say that numbers of applications from people already on the electoral register were high, ranging from an estimated 30% to 70% across the country.
Information is held locally, which means that duplicate applications are not automatically detected.
The watchdog called for the Government to look at introducing a system to allow electors to check if they are already registered and consider whether to adopt automatic registration schemes similar to the one used in Australia.
Electoral Commission chairman Sir John Holmes said: "The size of the registered electorate for the general election demonstrates the UK's strong tradition of democratic engagement, and reflects the hard work of all concerned.
"However, if we are to keep pace with modern habits and practice in a digital world, the electoral registration system must continue to evolve, and consider innovative solutions such as direct or automatic enrolment processes.
"These have the potential to deliver significant improvements to the accuracy and completeness of electoral registers as well as efficiencies for local authorities and the public purse."