Andrew Lloyd Webber has announced the cancellation of the opening night for his new musical, Cinderella, just hours before it was due to welcome the press and its first full-capacity audience. Uncertainty now hangs over the future of the show, which the composer says has been subjected to “the impossible conditions created by the blunt instrument that is the government’s isolation guidance”. Two preview performances of Cinderella were cancelled on Saturday as a precautionary measure after the testing system at the Gillian Lynne theatre in London’s West End identified a member of the cast in a small role who had Covid. In a statement on Monday afternoon, Lord Lloyd-Webber said that further tests had been carried out on backstage crew and on those due to perform on Monday evening, and that they had all been negative. Nevertheless, the production will now remain closed for the rest of this week due to the government’s Covid isolation instructions. Tickets for performances beyond this weekend are no longer available on the show’s website, which says they will go back on sale soon. A further announcement about the £6m musical’s future is expected in the next couple of days. Lloyd Webber said that they had been “forced into a devastating decision which will affect the lives and livelihoods of hundreds of people and disappoint the thousands who have booked to see the show”. There is rising frustration among theatres, who say that the current operating conditions are unsustainable. If a worker on a production is forced into isolation after testing positive for Covid or receiving a Test and Trace “ping” on the NHS app, it can bring down a show for several days without the safety net of insurance. The West End musical Hairspray and the Bridge theatre’s production of Bach & Sons, starring Simon Russell Beale, are among several major shows that have recently closed their doors for a number of performances shortly after opening. Equity, the performing arts workers’ union, released a statement saying it was “very saddened” to hear of Cinderella’s cancellation, and reiterating its request for the government to bring forward changes to the self-isolation rules for the performing arts and entertainment sectors in England. The government’s current plan is that, from 16 August, ​workers who come into contact with someone who has Covid only have to self-isolate if they test positive themselves. Cinderella began previews at 50% capacity on 25 June, after a delay of 10 months caused by the pandemic. Last month, Lloyd Webber declared himself ready to risk arrest and open for full-capacity audiences without the government’s go-ahead. But that action could have led to others on the production being fined, he later observed, so 19 July was set to be the date for Cinderella’s first full house. The composer has estimated a weekly loss of £100,000 on the show while the audience has been reduced for social distancing. The new musical has music by Lloyd Webber, lyrics by David Zippel and a book by Promising Young Woman’s Oscar-winning Emerald Fennell. Cinderella’s star, Carrie Hope Fletcher, tweeted that she was “completely and utterly gutted” about the cancellation. “Freedom Day,” concluded Lloyd Webber, “has turned into closure day.”