Chairman and CEO Michael Sweeney said in a statement that part of the company's decision to sell its stake in the building came from the significant investment needed to maintain the building's infrastructure and appearance.
"Due to the prominent siting of the advertisement within the Kensington Place conservation area, its elevated position on the buildings and its use of modern and incongruous materials the proposal fails to preserve or enhance the architectural of historic character and appearance of the conservation area and the appearance of the building and represents an unduly dominant and obtrusive advertisement, " the council said.
Council highways and property officials are preparing a list of works needed to "safeguard the integrity" of the building and to "improve its visual appearance".
Iconic because of its celebrated appearance in the cult British gangster film Get Carter, Trinity Square is a building that has polarised the architectural establishment, the media and locals alike.