Bristol City Council (BCC) has admitted its approval for plans to convert the derelict Whiteladies Picture House was unlawful.
Campaigner David Fells, who is seeking a judicial review of the decision, said the council had not properly followed national guidelines, leaving the building “vulnerable”.
Councillors unanimously approved plans in June which would see cinema operator Everyman join forces with owners Medinbrand to create a three-screen cinema. Five apartments would be built within the grade II-listed building as an enabling development.