LONDON—England is open to American visitors again.

The government said it would allow U.S. citizens, and those from most of the European Union, to enter England without quarantine requirements from Monday if they can demonstrate proof of being fully vaccinated against Covid-19, hoping for an influx of late-summer tourists.

The rules technically apply to England, not Scotland, Wales or Northern Ireland. But with no travel restrictions between those regions, the government is effectively opening up the whole country to visitors, as long as they arrive via England, home to the country’s biggest airport, Heathrow, which is also the main travel corridor to the EU.

The opening doesn’t apply to France, from which visitors will continue to require quarantine. The U.K. has singled out France for what it says is a high Covid-19 caseload.

U.K. officials, executives and tourism officials and workers are banking on American visitors to help save them from another summer devoid of visitors. The opening comes relatively late in the season, however. Many U.S. children will be back in school by mid-August, and the window for planning a European vacation may already be too narrow to attract a flood of Americans.

Still, Alex Beard, chief executive of London’s Royal Opera House, said the city’s famous theater district could gain. “Visitors from the United States are a hugely important part of the audience,” he said.

The reopening is also a boost for trans-Atlantic carriers that have been pushing governments on both sides of the ocean to reopen the world’s biggest travel corridor. For the likes of British Airways, owned by International Consolidated Airlines Group SA, and Virgin Atlantic Airways Ltd., the lifting of restrictions is key to their recovery. European airlines are more reliant on cross-border travel than peers in the U.S., which is experiencing a boom in domestic travel.

The easing, so far, is only one way. The Biden administration earlier this week said it would keep in place restrictions that prevent non-U.S. citizens from places including the U.K. and EU from entering the country because of rising cases of the Delta variant of Covid-19.

The Centers for Disease Control and Prevention last week moved the U.K. back to a level 4 risk category, indicating “very high” levels of Covid-19.

A passenger at London’s Heathrow airport, the U.K.’s biggest.

A passenger at London’s Heathrow airport, the U.K.’s biggest.

Photo: daniel leal-olivas/Agence France-Presse/Getty Images

Under the new guidance, most EU citizens issued with a digital health certificate that holds proof of a passenger’s vaccination records will be able to enter the U.K. freely, reopening a critical travel market for short-haul European traffic. U.S. citizens will be able to show their vaccination cards at check in.

British Airways and Virgin Atlantic both urged the U.K. government to go further by adding the U.S. to its so-called “green list” of countries, which allows all incoming travelers, regardless of vaccination status, to enter the U.K. without having to quarantine.

“With the U.K.’s Covid cases falling while vaccinations continue to rise, now is the time for the government to help secure the reopening of the crucial U.K.-U.S. travel corridor,” British Airways Chief Executive Sean Doyle said in a statement.

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Write to Benjamin Katz at ben.katz@wsj.com