A landmark mural in Hull which campaigners fought to save will have to be demolished because it is riddled with asbestos.
Hull Council said the latest survey had ruled against retaining the Three Ships mural on the former BHS and Co-op building as part of the £120 million Albion Street development.
After removing loose asbestos, contractors have discovered that there is also asbestos - unusually - in the concrete sub-structure.
The council said plans to remove and replace the 1963 mural, designed by Wolverhampton artist Alan Boyson, is no longer possible, as it would breach health and safety regulations and pose a risk to public safety.
The 66ft by 64ft Italian glass mosaic mural - thought to be one of the largest in the country - immortalises the Hull fishing fleet.
More than 6,500 people signed a petition to save it after it was first threatened with demolition.
A briefing heard that the building is “contaminated from the internal elements right down to the sub structure and superstructure.” The council’s deputy leader Coun Daren Hale said “safety had to come first”,
He said: “We started out on this journey, putting a degree of money aside for reports, with the aim of retaining the mural - planning permission was based on that.
“We knew at the time that we bought the building and got various grants that it had asbestos - all buildings of that era have it normally in the panelling, the soffits.
“Once the contractors removed that they found dangerously high asbestos levels in the substructure, in the DNA of the building, the concrete.”
Another “Fish” mural, also by Boyson, is salvageable, but the “jury is still out” on a third inside, which has been damaged with emulsion paint, Coun Hale said.
He said high-resolution pictures had been taken so the image of the mural could be “sympathetically replicated” on the front of the new development.
Leigh Bird, from Hull Heritage Action Group, said they were devastated. She said: “There will be a lot of pressure on the council to make sure that what replaces the Three Ships is done in a proper, sensitive and celebratory way.
“It wasn’t originally intended to be a memorial but it became part of the city’s heritage.”
Albion Square includes a new home for Hull’s Ice Arena, 270 homes and nearly 182,000 sq ft of retail.
The council said demolition of the BHS building will start next year, overseen by the Health and Safety Executive and the building may have to be shrouded in a “huge wrapper”.
Funding from the Homes and Community Agency and the Local Enterprise Partnership “should cover” the extra costs - which will include all the rubble having to be taken away from the site and be treated as contaminated waste.