Campaigners claim around £2 million could secure the future of the boarded-up site on Lothian Road, which has been put up for sale by administrators.
It warns the city’s international reputation as a cultural capital and its cinematic heritage would be damaged if the Filmhouse building was to be lost forever.
The open letter also raises concerns that efforts to revive the Edinburgh International Film Festival (EIFF) would be threatened if the city lost the Filmhouse.
It is described as the UK’s “best equipped cinema” after the BFI Southbank, which organises the London Film Festival.
The official campaign was set up to “demand fair treatment for staff and fight for the future of the Filmhouse and independent cinema in Edinburgh”.
Backers include Rod White, the Filmhouse’s long-time head of programming, Kristy Matheson, the creative director brought in for this year’s festival, former festival director Mark Cousins and Ginnie Atkinson, former managing director of the Filmhouse and the EIFF.
The letter has emerged just days after the converted church building, which has been home to the Filmhouse since 1978, went onto the open market.
The document states: “As you know, the Centre for the Moving Image (CMI) went into administration on October 6.
"The converted church at 88 Lothian Road is up for sale to pay off the debts of the CMI. Time is of the essence. It is to be sold – on or before December 6 and it will be the administrator, who does not need to consider what their decision means for the city and its residents, who decides who the buyer is.
“We’re calling upon the Scottish Government and council to buy the Filmhouse building at 88 Lothian Road. If the Filmhouse goes, it means Edinburgh – one of the pre-eminent cultural capitals of the world – would be without a home for cultural cinema.
“Other cities in Scotland and in the UK have them and I’m sure you will agree it is unthinkable to not have such a cinema in Edinburgh, a city with a rich film heritage, which includes one of the oldest film festivals in the world and the oldest extant film guild/society, both now collateral damage in the demise of the CMI.”
The CMI collapsed weeks after the EIFF was given £270,000 in additional funding from the Scottish Government to help mark its 75th anniversary. The event, which was established the same year as the International Festival and the Fringe, has used the Filmhouse as its headquarters in modern times.
Warning about the potential impact of the Filmhouse building being acquired for commercial purposes, the open letter adds: "The Edinburgh International Film Festival, who have always put their more complex presentations in Filmhouse, would not meet the expected standards of technical delivery without this superb facility, which is a cinemathèque of national standing.
"Filmhouse has always been the perceived heart and hub of EIFF and its loss would be monumental. Outside of the BFI Southbank, Filmhouse is the best equipped cinema in the UK.
"It can show films on all manner of formats, including 35mm and 70mm, and has equipment that allows films to be exhibited properly from any suitable digital format. Its 30 or so programme partners have benefited greatly from this capability over many years."
The Filmhouse building, which is expected to be sold to the highest bidder, is being described as a “unique leisure-development opportunity” by agents handling the sale. Savills say the property would be “suited to a number of alternative uses, subject to obtaining the necessary consents”.
However, more than 23,000 people have backed an online petition calling for the EIFF and the Filmhouse cinemas in Edinburgh and Aberdeen to be saved. Images from classic films were projected onto the facade of the Filmhouse building last week as part of the campaign to save the city’s cinematic institutions.
The open letter states: "Filmhouse could be saved. In the region of £2m would secure a future for cultural cinema provision in Edinburgh. If 88 Lothian Road is lost, any alternative new building or premises would cost many, many times more and seems an unlikely prospect at any time, let alone in the current economic climate.
“Edinburgh could be without cultural cinema provision for a generation. The technical set up in Filmhouse, built up over many years, will likely be lost forever. We may never get it back. Buy the building now and the future of cultural cinema in the nation’s capital is secured.
“A Filmhouse run for its own sake – without any of the financial burden placed upon it by the CMI structure – would, arguably, be an entirely sustainable enterprise, with no more public subsidy required than was ever the case.”
A spokeswoman for the Government said: “Ministers are concerned at the situation facing the CMI and the implications this has for its staff, as well as for Scotland’s creative and culture sector.
"The Scottish Government and Creative Scotland are engaging with the CMI administrators and partners to explore options for cultural cinema programme activity in both Edinburgh and Aberdeen, as well as a 2023 edition of the Edinburgh International Film Festival.
“It would not be appropriate for the Scottish Government to comment on ongoing legal proceedings. The sale of the Filmhouse in Edinburgh is now in the hands of the administrators.“
A spokeswoman for Creative Scotland said: “With the Filmhouse building being offered for sale by the administrators, we hope a buyer can be found who will continue operating the building as a cultural cinema.”