The sector has been hit by a series of Covid-forced show cancellations.
Dame Rosemary, joint chief executive of Trafalgar Entertainment alongside Sir Howard Panter, said the “virulent” new strain of Covid-19 is “causing huge disruption and irreparable damage to an already fragile theatre industry”.
Trafalgar Entertainment is the second biggest theatre company in the UK, taking in the Trafalgar Theatre in the West End, the new Olympia Theatre in west London and HQ Theatres, which has a portfolio of around 14 regional venues.
Dame Rosemary said: “Whilst we are doing everything we can within our theatres to protect staff, customers and performers through robust safety measures, the virulent Covid Omicron variant is now causing huge disruption and irreparable damage to an already fragile theatre industry.
“In what would usually be our busiest time of year, we are now sadly witnessing cancelled performances across the board and outbreaks of Covid amongst casts and production staff.
“This, coupled with the confusing and contradictory Government messaging, is causing consumer confidence to plummet.
“The Government must act now and offer financial support and compensation to our world-beating theatre, live entertainment and hospitality industries or we will struggle to survive. Our industries depend on each other, but we can’t do this alone.”
On Monday, Boris Johnson warned that new controls could be brought in to curb the spread of Omicron, saying data is being monitored “hour by hour” amid fears the NHS could be overwhelmed.
The Prime Minister also said the economic impact of any new measures needs to be taken into account – particularly those sectors which are already struggling due to the pandemic.
He said: “There are still some things that we need to be clearer about before we decide to go further.
“It is important we act cautiously but it is also important we look after the hospitality industry, the theatres and other parts of our incredible entertainment industry which have suffered and are suffering.”
His comments followed a string of cancelled theatre performances, with The Lion King in the West End dimming its lights until at least December 28 due to “ongoing Covid-enforced absences” among cast and crew.
Other London-based musicals including The Book Of Mormon, Cabaret At The Kit Kat Club, Dear Evan Hansen and Come From Away have announced they will also all be suspended until late December.
Dame Rosemary said lifeline schemes that were “only very recently switched off” by the Government could “easily be reinstated”.
She called for measures including a return to 5% VAT on ticket sales and business rates relief on cultural buildings, as well as the reintroduction of the furlough and job retention schemes and a widening of the eligibility criteria to the Culture Recovery Fund (CRF) to allow bodies that previously received money to reapply.
The £1.57 billion CRF was launched in July 2020 with the objective of protecting Britain’s cultural, arts and heritage institutions.
Dame Rosemary added: “Covid and its doubtless many variants will be around for many years, so we all need to find ways to live with it.
“And, as we look ahead to 2022 and beyond, our industry will continue to face these challenges, and we must all be prepared to adapt, innovate and reassure.”
She ended by saying another lockdown “without the appropriate financial support in place would be disastrous”.
“Tens of thousands of jobs, livelihoods and people’s mental health depend on it,” she said.
“The economic impact would be huge. We cannot be left in such a critical state. Theatre is a refuge and a joy in times like these – we need to protect it.”
Sir Cameron Mackintosh, whose theatre productions include Hamilton, Les Miserables and Miss Saigon, told BBC News on Monday night that the Government needs to “step in and help the commercial theatre, because by and large the commercial theatre hasn’t had any help at all across the pandemic”.
A spokesman for the Department for Digital, Culture, Media and Sport said: “Our unprecedented £2 billion Culture Recovery Fund has given out £1.5 billion in grants and loans.
“The £300 million third round of the Culture Recovery Fund is still open for applications, providing vital ongoing support for the arts, heritage and creative sectors.
“We will keep the delivery of the programme under review and consider how best to adapt it in line with need.
“We recognise how important the festive period is for so many businesses and the Government will continue to engage constructively on how it can best provide ongoing support to those affected.”