The business will now take its case before the Royal Court in an attempt to get the decision overturned.
Last month, the planning applications panel rejected the scheme, which included the demolition of four of six historic buildings in the area and the building of offices, an extended store and new ground-floor shops.
Following the refusal of their scheme Co-op representatives said they felt they had been treated appallingly by the Planning department, which they claimed had offered conflicting advice as the scheme evolved.
