The British government said on Thursday that it would allow 16- and 17-year-olds to vote, in what it called a landmark moment for democracy and some of its opponents decried as an attempt to tilt the electoral playing field.

Britain has more than 1.6 million people of age 16 or 17, in a total population of roughly 68 million, and the plan has been described as the country’s largest expansion of voting rights in decades. The last nationwide reduction in voting age, to 18 from 21, came more than 50 years ago.

“Declining trust in our institutions and democracy itself has become critical, but it is the responsibility of government to turn this around and renew our democracy, just as generations have done before us,” the deputy prime minister, Angela Rayner, wrote in an introduction to a policy paper that included the announcement.

The plan also includes promises to tighten laws on foreign donations to political parties, and to simplify voter registration.

Here’s a guide to the change and its implications.

Do many places give 16-year-olds the vote?

Several nations do, including Austria, Malta and Brazil, while in Greece the voting age is set at 17. Others allow 16-year-olds to participate only in some elections: In Germany and Belgium, they can help choose members of the European Parliament, but they cannot vote in federal elections. Britain has been in that category: Elections for the separate parliaments that control many policy areas in Scotland and Wales already had a voting age of 16.

Is this change a surprise?

No. The center-left Labour Party has backed votes for 16-year-olds for some time, and the idea was part of the official platform on which it won last year’s general election.

Will it definitely happen? How long will it take?

The move requires a law, which will have to get through both houses of Parliament, so this change is some way off. But Labour has a large majority in the elected House of Commons, and the appointed House of Lords traditionally restrains itself from interfering with election promises. There’s plenty of time, too: The next general election is not expected until 2029.

Is 16 a standard age limit in Britain?

The government points out that 16-year-olds in Britain can leave school, work, pay taxes and join the military. Critics of the voting age change note that 18 is the legal minimum age to run as a candidate in an election, to take part in armed combat in the military, to marry and to buy alcohol or a lottery ticket.

Does Britain need to worry about participation in elections?

There are some worrying signs. Turnout at the 2024 general election was 59.7 percent — the lowest since 2001 and 7.6 percentage points lower than in the previous general election in 2019. “Our democracy is in crisis, and we risk reaching a tipping point where politics loses its legitimacy. The government has clearly heard these alarm bells,” said Harry Quilter-Pinner, executive director of the left-leaning Institute for Public Policy Research.

Which parties might appeal to 16-year-olds?

Polls in Britain have long showed younger voters skewing left. So Prime Minister Keir Starmer will hope that his center-left party benefits — and the Greens might also expect a lift. Paul Holmes, a senior lawmaker for the main opposition Conservative Party, described the plans as a “brazen attempt by the Labour Party, whose unpopularity is scaring them into making major constitutional changes without consultation.”

But some recent polling has found growing support among young people for Reform U.K., a new right-wing populist party led by Nigel Farage that is strongly anti-immigration. One survey earlier this year showed almost one in five of 18-to-24-year-olds favored Reform, although Labour was still ahead with this age group. Far-right parties in some other European countries, notably France, have claimed growing support among young people.

Also worth noting: The last cut in voting age, in 1969, was also implemented by a Labour government — which then lost the subsequent election.

How else could the plans increase voter participation?

The government says it will create a more automated voter-registration system, reducing the need to provide personal details for access to different government services. It will also expand the range of documents that voters can use as proof of identity to include payment cards issued by British banks.

Why does the government want to restrict foreign political donations?

There was speculation late last year that the technology billionaire Elon Musk might donate to Reform U.K., though he then cooled on Mr. Farage. But that episode raised concerns with some lawmakers about foreign interference in British elections. In the proposals outlined on Thursday, the government said it would tighten checks on some donations and prevent a foreign donor from setting up a shell company in Britain to channel cash to a political party.