Andrew Lloyd Webber has joined others in the entertainment industry in launching legal action to force the Government to hand over the results of its pilot live events.
The Events Research Programme ran test events at sporting, music and arts venues to assess the safety of large gatherings during the pandemic.
In a statement, the group, which also includes musician Peter Gabriel and theatre producer Sir Cameron Mackintosh, accused the Government of "making it impossible to plan for any live entertainment business" by not sharing their findings.
Lord Lloyd Webber previously told The Telegraph that police would have arrest him if they wanted him to stop reopening.
On Thursday he said: "Last week I rejected the Government’s invitation for Cinderella to be singled out as a last-minute part of the Events Research Programme.
"Today, with a range of voices from across the theatre and live entertainment industries, we are forced to take it further.
"We simply must now see the data that is being used to strangle our industry so unfairly.
"The Government’s actions are forcing theatre and music companies off a cliff as the summer wears on whilst cherry-picking high-profile sporting events to go ahead. The situation is beyond urgent."
Sir Cameron said: "Having been forced to close our theatres twice last year, the second time after the Government encouraged reopening for Christmas, losing further millions as a result, a joint insurance scheme to protect us against another enforced closure is vital.
"Along with most of the commercial theatre we have had absolutely no direct financial help either for our productions or the upkeep of our historic theatres.
"Opening without any sort of protection is impossible for many producers, live event organisers and theatre buildings across the country.
"Having contributed huge amounts of money to the exchequer over the last few decades, the theatre desperately needs to be supported in its hour of need or the government will be responsible for the disintegration of one of this country’s most priceless and irreplaceable assets after centuries of being the envy of the world."