The boss of the Edinburgh Festival Fringe has intervened in the row over the future of the Assembly Rooms by calling for refurbishment plans to be put on hold.
Kath Mainland, chief executive of the festival, has urged the city council to settle a dispute with the promoters who run shows at the venue before starting any work at the A-listed building.
She wants the local authority to work with Assembly Theatre to find an amicable solution to the row over the controversial plans, which would see the landmark close for 18 months for a 9.3 million revamp.
She has paid a glowing tribute to the promoters, who have been accused by the council of waging a "dangerously misleading" campaign against the proposals. Ms Mainland claims they have "carved out a unique place in the Fringe" over the past 30 years and warned that the festival needed a strong geographical mix of venues which could produce work on different scales.
Fears have been expressed that the New Town will be left without a flagship venue if the refurbishment plans go ahead.
More than 5,700 people have backed an online campaign to halt the refurbishment, including comedy stars who have performed at the venue, such as Johnny Vegas. The promoters will be making a last-ditch plea to councillors next week to shelve the project after the authority's head of planning banned any debate when the council's own application was heard earlier this week.
The council insists urgent action is needed to secure the future of the Assembly Rooms, which it claims are in "desperate" need of repair, and that the shops and "destination" restaurant will help pay for the restoration of the rest of the building, which dates from 1784.
Five of the smallest theatre spaces face being lost during the Fringe under plans to create shops and a fine-dining restaurant. The council insists the changes will help ensure the building is used all 52 weeks of the year and has also threatened to bring in another promoter to run Fringe shows there.
Ms Mainland said: "It is important to the overall vibrancy of the Fringe that there is a healthy mix of different venue operators and producers. It is also important that venues are spread over as broad a geographical base as possible and that there is a mix of venues who can present and produce work of differing scales."We recognise the need to restore the building, both for the long-term, year-round use, and to ensure its continued place as a vibrant Fringe hub and iconic Edinburgh city venue.
"We look forward to all parties finding a solution that ensures that best possible outcome for all users of the building and which sees a refurbished Assembly Rooms continuing to host exciting and entertaining work for the audiences of the Fringe."
William Burdett-Coutts, artistic director at Assembly Theatre, said: "We are planning to go to the full council meeting next week to present the petition and make a final case.
"We hope the council will still see sense, even at this stage."
However, a spokeswoman for the council said there was no question of the project being delayed because of the need to have the building ready for the 2012 Cultural Olympiad.
Festivals and events champion Steve Cardownie said: "We've already had serious interest from promoters who want to take the building on during Festival time once the refurbishment is complete, and we're confident there will be very healthy industry competition for this much-sought-after Festival address."