Their problems echo those across society as the Ukraine war and its impact on energy supplies have exacerbated a cost-of-living crisis in Britain, where inflation rates are among the highest in the developed world.
People want escapist fun more than ever, and musicals and Christmas shows are drawing record audiences, but attendance figures for the year overall lag pre-pandemic levels and pantomime jokes about utility bills generate nervous laughter.
Steve Mannix, executive director at the Mercury Theatre in Colchester, to the northeast of London, says half in earnest that he has told the cast of "Beauty and the Beast" to stick to the script for fear of running over time: the emergency back-up generators waiting in the wings have only three hours of capacity.
"In 37 years in this industry, this is the hardest," Mannix said.
Even after a 14 million pound ($17 million) refit to install triple glazing, low energy lights and solar panels that has put the theatre in the country's top 25% of environmentally-friendly public buildings, Mannix says its cash reserves will run out in six months' time unless the government provides more help.
The Mercury Theatre's annual energy bill is set to reach 120,000 pounds ($147,432), up from 40,000 pounds last year.
It cannot pass on the extra cost, in part because many tickets were sold months in advance, and in part because theatre-goers have limited cash to spare.
"We know this is a difficult time for theatres and we remain firmly on their side," a government spokesperson said by email, without specifying whether energy and tax relief for the arts would be extended.
The relief is currently expected to decrease at the start of April.
Figures vary as some London theatres benefit from tourists lured by sterling's weakness while classical music and more experimental theatre suffer the biggest audience declines.
But overall, tickets sales for some of the country's top theatres were down 38% in the three months to August from the pre-COVID average, according to data providers The Audience Agency. A brief improvement earlier this year vanished as the cost-of-living crisis took hold.
Nine out of 10 theatres are worried for their future, with eight out of 10 saying they need deep cost cuts to survive, research commissioned by Ecclesiastical Insurance and shared with Reuters showed.
Theatres rely on insurance in case of cancellation, for instance because of blackouts, though premiums have also risen.
Ecclesiastical commissioned research by OnePoll, which interviewed representatives of 100 theatres and found nearly half were renegotiating suppliers' contracts, reducing opening hours and reducing staff hours.
Even the big private theatre groups are worried.
Trafalgar Theatres, which operates 13 venues across Britain, including in London, said in emailed comments it had so far seen a 200% increase in energy costs.
"Theatre operators are having to look at all costs and all revenue streams to remain viable," it said.
In the small independent venues, where budgets have always been stretched to breaking point, the battle to survive continues.
"Energy strategy - we bought some hot water bottles. That's about it. We're just struggling on," said Neil McPherson, artistic director at the Finborough Theatre based in a west London pub.
($1 = 0.8139 pounds)