The arts are at the “point of no return” following damage from the coronavirus pandemic, Lord Lloyd-Webber has said.
The composer and theatre impresario told MPs that it would be economically “impossible” to run theatres with social distancing.
“We simply have to get our arts sector back open and running,” he told the Digital, Culture, Media and Sport Committee.
“We are at the point of no return.”
In July, Lord Lloyd-Webber staged a concert at the London Palladium as an experiment to see whether socially-distanced performances were viable.
He spent £100,000 on the pilot project in the hope that it could allow the theatre business to get up and running.
He had originally hoped to show that theatres can open at full capacity safely.
However, the concert had to take place with hundreds of empty seats, to comply with the government’s social distancing guidelines.
Since then, two major new indoor theatre productions have opened in London, but also with limited audience capacity.
The Talking Heads monologues at the Bridge Theatre and Sleepless at the Troubadour in Wembley Park have recently opened their doors.
However, most other theatres, including those in the West End, are yet to re-open.
“There comes a point now when we really can’t go on much more,” Lord Lloyd-Webber said.
“Theatre is an incredibly labour-intensive business. In many ways putting on a show now is almost a labour of love.
“Very few shows hit the jackpot in the way a Hamilton, Lion King or Phantom Of The Opera do.”
He added that theatre productions are “not like cinema, you can’t just open the building”.
The government announced a £1.57bn support package earlier this year to support the arts, which was widely welcomed by the industry.
But Lord Lloyd-Webber stressed the importance of naming a date theatres can re-open.
Lord Lloyd-Webber also discussed the “critical” importance of clean air, adding that the air inside his theatres is cleaner than it is outside.
“I am absolutely confident that the air in the London Palladium and in all my theatres is purer than the air outside.”
He also suggested he could move his production of Cinderella from the UK to a different location “where people are being a little more helpful”.
It was originally due to open in London’s West End this month.
Rebecca Kane Burton, chief executive of Andrew Lloyd Webber’s venues LW Theatres, said: “We don’t want to open theatres on a socially distanced basis. I have no intention of opening buildings at 30% capacity.”
She said recent months had been “devastating and catastrophic” for the sector.
“It’s a really bad, catastrophic time and we need to find a way out of it,” she said.
“It was disheartening that the pilot wasn’t later seen as a way to getting full re-opening.”
She added: “We need the time to plan. We can’t switch on theatre like a tap. Christmas is hanging in the balance as we speak.”
Writing in the Mail on Sunday at the weekend, Culture Secretary Oliver Dowden said the government was currently working on a project which would see some theatre return in time for pantomime season at Christmas.
“My officials are working on ‘Operation Sleeping Beauty’ which aims to bring back some of the magic of theatre for families this Christmas, and I hope to share more progress soon,” he said.
Mr Dowden also suggested rapid testing could help ensure the return of theatres.
“Testing is the short-term key until we find a working vaccine,” he said.
“We’re making exciting advances in quick turnaround testing, where on-the-day coronavirus tests could give people who test negative a pass to visit the theatre that evening.”
Lucy Noble, artistic and commercial director of the Royal Albert Hall and chair of the National Arenas Association, told the DCMS Committee there were “huge consequences to venues not being able to put performances on… serious financial consequences”.
She added: “All venues are on their knees financially… When Oliver Dowden announced the £1.57 billion rescue package, the Royal Albert Hall was hailed as one of the crown jewels that this package would save.
“We have been told we are not eligible for any of the grant at all.
“We are only eligible to take a loan. We’ve already taken £10 million worth of loans. We’d rather not get into any more debt.”