Voters in U.K. Cast Ballots Online, in Test for Internet Voting

The Conservatives are sending qualifying members a ballot pack in the mail that will include a paper ballot to be returned by mail and information and security codes for voting online. “We recommend online voting where possible,” the party states on its website.

The party sought guidance from Britain’s National Cyber Security Centre, or NCSC, and a Tory spokesman said the party was confident the leadership election would be secure. “We have consulted with the NCSC throughout this process,” the spokesman said.

Election security analysts fear the system is vulnerable to interference by hackers.

“We do not have the technology to conduct voting securely online and so it should not be deployed for high-stakes elections,” said Peter Ryan, a professor of applied security at the University of Luxembourg. “And I count this as rather high stakes.”

Internet voting of any variety has long been considered off-limits in the U.S. by most cybersecurity experts and election officials. Ahead of the 2020 presidential election, federal agencies privately warned states that voting over the internet would pose a high cybersecurity risk and was vulnerable to disruption, The Wall Street Journal has reported.

The warning came as some U.S. states considered expanding online voting amid the coronavirus pandemic. The federal agencies drew a distinction between the electronic delivery of blank ballots to voters, which it rated a low risk, and enabling voters to return completed ballots electronically, a high risk.

No U.S. state permits all of its voters to cast a ballot online, but some allow overseas, military voters or disabled voters to do so. In addition, some states send blank ballots electronically for voters to print and return by mail.

The British leadership contest is now a two-person race between Foreign Minister Liz Truss and Rishi Sunak, the former treasury chief, who are vying to replace Prime Minister Boris Johnson, who was ousted in July after a series of scandals. Opinion polls show Ms. Truss with a large lead.

Conservative lawmakers narrowed the field of candidates in previous rounds of voting this year, and some 160,000 rank-and-file members of the Conservative Party will be eligible to choose between the two candidates. (By contrast, 158 million voters cast a ballot in the 2020 U.S. presidential general election.) The winner will become the next prime minister.

In the British system of government, the ruling party can change prime minister without a general election. Though the leadership vote will be decided by a fraction of the British electorate, it is one of the few examples in which a democratic country has permitted all eligible voters to choose a new head of government by casting a ballot over the internet. Britain’s Labour Party has allowed online voting in recent leadership elections as well, but to choose an opposition leader, not a prime minister.

Other countries including Canada and Switzerland have explored broad online voting but have either halted or curtailed it over security concerns, said Dan Wallach, a computer science professor at Rice University who has researched the issue.

An electronic voting system in Estonia has for more than a decade been seen as a rare outlier. In the Baltic nation of about 1.3 million people, the voting is linked to a mandatory national identification card and has various transparency and security protocols.

Advocates of online voting in the U.S. and elsewhere say the method could boost turnout, trim costs and help disabled and overseas voters, though they acknowledge some security risk is unavoidable.

Some security experts say secure, broad online voting might one day be achievable. Mr. Ryan has been working on developing standards for two decades for in-person and online voting, but said no one has developed a way to make online voting acceptably secure and private.

“For the moment, short of a major conceptual breakthrough, I don’t see how it can be done,” Mr. Ryan said.

The U.K. leadership election is being held by the party itself, rather than by local officials who generally manage voting in general elections or Britain’s Electoral Commission, a national agency that provides best practices guidance and oversight.

The security agency told the Conservative Party there was no way to eliminate all risk by allowing online voting as an option in the election, a person familiar with the matter said.

Write to Dustin Volz at dustin.volz@wsj.com