Many London theaters are canceling performances, and people in the industry fear that more productions will have to close when England ends distancing and mask-wearing requirements next week.LONDON — The cast and crew of “Seven Methods of Killing Kylie Jenner,” an experimental play at the Royal Court, were just two weeks into their run when they received some bad news: One member of the company had tested positive for the coronavirus, and everyone had to quarantine.On July 4, the theater canceled performances for a week.The next day, the producers of “Hairspray” at the London Coliseum announced that they were canceling nine days of shows, because a member of the production team had tested positive, and later that week the Globe called off a performance of “Romeo & Juliet,” because an actor in the show had, too.This Monday alone, “The Prince of Egypt” at the Dominion Theater; another “Romeo & Juliet,” at the Regent’s Park Theater; and “Bach and Sons,” at the Bridge were all canceled for at least five days because of confirmed or potential cases.The spate of abandoned shows comes at what was supposed to be a celebratory moment for British theater. Starting Monday, playhouses in England will be allowed to open at full capacity for the first time since the pandemic began, as the country ends restrictions on social life in an effort to restore normalcy while living with the virus. Audience members will no longer have to wear masks inside theaters, although many are encouraging patrons keep them on.Yet with coronavirus cases soaring in Britain because of the more contagious Delta variant, theaters fear more cancellations, given that many young actors and crew members are not yet fully vaccinated. “We are all ready for it to happen again,” Lucy Davies, the Royal Court’s executive producer, said in a telephone interview. “It’s going to be fragile all summer.”“The Prince of Egypt,” at the Dominion Theater, shut down on Monday along with two other London shows.Matt CrockettCalled-off shows will cause further financial stress on cash-strapped theaters, Davies said, especially because no commercial insurers in Britain offer cover for coronavirus-related cancellations. And producers say the British government’s coronavirus rules are part of the problem. When people test positive here, they are required to quarantine for 10 days, as must all of their “close contacts” — defined as anyone who has been within about six feet of an infected person for 15 minutes.In Britain, more than 42,000 new coronavirus cases were recorded on Wednesday, a number last seen in January when the country was in lockdown to prevent its health system from being overwhelmed. Sajid Javid, the health minister, said on Monday that daily numbers were likely to rise to over 100,000 a day during the summer, although hospitalizations and deaths are expected to be much lower than in previous waves of infection, because two-thrids of adults have been fully vaccinated.In the first week of July, more than 520,000 people in England were told to quarantine as close contacts, according to official figures. They have to isolate even if they test negative for the virus or have had two vaccination shots.Eleanor Lloyd, a producer who is the president of the Society of London Theater, said that most of the cancellations were because of close contacts who were told to isolate, rather than positive cases.The Regent’s Park Theater said in an emailed statement that several of its staff members had been told to stay at home and were still in quarantine, despite later testing negative. “We do need an alternative to automatic self-isolation for our acting company and crew, as the current situation is simply unsustainable,” the statement said.Starting Aug. 16, fully vaccinated close contacts will no longer need to quarantine. “It’ll be better from then,” Lloyd said. But that is still a month away, and the risks may continue longer. So she is considering employing more understudies for a forthcoming production of Agatha Christie’s “Witness for the Prosecution.” That would have a cost, too, she said.London theaters have adopted safety measures to try to limit the risk of outbreaks. In most, casts and crew are tested several times a week, and masks and distancing are typically required offstage. But “people are traveling to and from the theater, and that is a risk, however safe our environment is,” Davies said.Joel MacCormack and Isabel Adomakoh Young in the title roles of the Regent’s Park Theater production of “Romeo and Juliet.” The show’s producers also had to call off performances.Jane HobsonThe safest productions seem to be those created especially for these pandemic times, with social distancing among the players both onstage and behind the scenes. The Globe has used this approach for shows like its “Romeo & Juliet.”Even so, last Saturday, Will Edgerton, who is playing Tybalt, learned that he had the virus after performing a home test.The Globe canceled that afternoon’s show so that a new actor could rehearse the role, then went ahead with the evening performance. “We are unique, as Shakespeare’s plays can be presented with distancing,” Neil Constable, the theater’s chief executive, said in a telephone interview. “But when you’ve got a major musical like ‘The Prince of Egypt,’ which costs millions of pounds and has lots of people onstage, you don’t have that option.”He said the British government should underwrite theaters’ risks, a sentiment that echoes calls by other leaders from Britain’s theater industry for a state-run insurance program. Last year, the government introduced a similar initiative for TV and movie shoots, but it has not announced anything for other forms of cultural life, as European governments like those of Germany and Austria have done.“We understand the challenges live events have in securing indemnity cover and are exploring what further support may be required,” a spokeswoman for Britain’s culture ministry said in an email.Davies, the Royal Court executive, said a safety net was badly needed, especially for commercial theaters that don’t receive public subsidies.She had a recent experience of the benefits of insurance, she said. On Monday, the cast and crew of “Seven Methods of Killing Kylie Jenner” were scheduled to return to the stage for their first performance since completing their quarantines — but then a severe storm flooded the theater’s basement and the show was canceled again.“It was devastating — it was their comeback,” Davies said, before adding that the theater’s insurers had covered some of its losses that night. “We’re insured for flooding,” she said, “just not Covid.” More