Britain’s theatergoers cover up again, after months without masks.

Since England’s theaters reopened without restrictions in July, one thing has been as notable as the action onstage: the lack of masks in the audience.

Unlike in Broadway theaters, patrons here have not been required to wear face coverings, and many attendees have chosen to ignore preshow announcements encouraging them to mask up.

Several visiting theater critics have been left aghast. Laura Collins-Hughes, writing in The New York Times in September, said that at “nearly every production I saw, there were loads — sometimes a majority — of barefaced people in the crowd, which felt reckless and delusional.”

Peter Marks, writing in The Washington Post in November, called London’s theaters “consistently shocking these days.” That had nothing to do with the action onstage, he added; it was entirely down to the absence of masks.

Now, that image may be about to change. On Saturday, Prime Minister Boris Johnson made masks mandatory in stores and on public transportation in England, responding to the newly discovered Omicron variant of the coronavirus.

He did not make them mandatory in theaters, but several venues have now done so voluntarily. On Monday, the Royal Shakespeare Company said face coverings would be required at its theaters in Stratford-upon-Avon, England, unless an attendee is under age 12 or has a medical exemption.

“We want to do all we can to ensure that we do not have to cancel performances and disappoint our audiences,” the company’s executive director, Catherine Mallyon, said in a news release.

Other theaters quickly followed. On Monday, Andrew Lloyd Webber, the composer and theater impresario, quietly strengthened rules for the six theaters he owns in the West End. His company website was updated to say, “All audience members must wear a face covering throughout their visit, except when eating and drinking, or if they are medically exempt.” Previously, those theaters requested masks, but did not require them.

On Tuesday, the National Theater, the Royal Opera House, the English National Opera and the Old Vic also said they would make masks mandatory.

The rules might only last a few weeks. The National Theater’s website says the measure will be in place until Dec. 19, “when the next government review of Covid measures is due.”

So far, there appears to be little resistance to the changes. Kate Evans, a spokeswoman for the Royal Shakespeare Company, said 45 people had asked for refunds or to exchange their tickets for vouchers to see a future show since the mandate was announced, out of 6,000 who had booked to see its current show, “The Magician’s Elephant.”

“The majority of feedback we’ve received around the decision has been very positive,” she said.