Opening night shows on Monday and Tuesday were cancelled. The composer announced the news on Twitter Monday, the same day that theaters and venues were allowed to fully reopen.
"Today, on this 'Freedom Day,' I have been forced to take the heartbreaking decision not to open my Cinderella," Webber said.
Webber described the play's rigorous testing system and how everyone on the crew had tested negative after a cast member who has a cameo role tested positive.
"Despite this, the impossible conditions created by the blunt instrument that is the government's isolation guidance, mean that we cannot continue. We have 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," Webber said.
"Cinderella was ready to go. My sadness for our cast and crew, our loyal audience and the industry I have been fighting for is impossible to put into words. Freedom Day has turned into closure day," he continued.
Carrie Hope Fletcher stars as Cinderella in the musical, an updated telling of the fairy tale by Emerald Fennell with music by Webber and lyrics by David Zippel.