Opponents have warned classic views of the city will be marred an extra level of shops, bars and restaurants is allowed to be built by new owners of the site.
Real estate firm Moorgarth unveiled plans last month for the expansion, which would see a new “superstructure” created to house commercial units around a “European market-style piazza.”
However the Cockburn Association, the city’s long-running heritage watchdog, has warned that protected views of the Old Town, Arthur’s Seat and the Waverley Valley will all be affected.
In a formal objection to the city council, which could trigger a public inquiry, its director Terry Levinthal has warned that such views are “much more important to the city than this development.”
However the developers insisting that “magnificent” views of the Old Town will still be able to be enjoyed from with its expanded complex.
Moorgarth claims its plans would also return the site to its Victorian market roots and create a “greater sense of arrival into Edinburgh” from Waverley Station, which is connected to the mall.
The developers claim the current complex is saddled with a “disjointed and poorly monitored” roof space dating back to the last major redevelopment in the early 1980s.
The firm claims: “This has resulted in what has been proven to be a less than successful urban space and a poorly performing retail space which neither gives the benefits of a proper garden contributing to the urban realm nor provides an appropriate retail experience for this high-profile location.
“The scheme has been designed by local architects with an in depth understanding of the heritage issues associated with the site, as well as a local advisory team with in-depth knowledge of the building and its importance in Edinburgh’s landscape.”
The stand-off between the developers and the Cockburn has echoes of the long-running battle over plans to add modern extensions to the former Royal High School on Calton Hill to accommodate a luxury hotel development. Although an operator, Rosewood, was announced three years ago, its fate will be decided at a public inquiry due to get underway later this year.
Mr Levinthal has told the council: “Whilst the Cockburn understands the challenge in improving the current mall, and the desire of the operator/developer to make the building more visible, the views across the Waverley Valley are much more important to the city than this development.
“The truncation of views from East Princes Street and approaches from St Andrew Square will affect the legibility of this separation and cause serious damage to the World Heritage Site. Similarly, views from the west towards Arthur’s Seat will be substantially affected.
“The proposals would adversely affect the character and appearance of both the New Town and Old Town conservation areas by visually interrupting the key visual interplay between the two, and therefore harming the character of each.
“We can see no means of mitigating this impact if building upwards is proposed.”
Moorgarth chief executive Tim Vaughan said: “Central to the proposals is ensuring that they fully integrate and enhance the surrounding area and public realm, whilst continuing to preserve the views over the Waverley Valley.
“Importantly, these new proposals remain one metre below the legally established height restriction that protects the view of the Waverley Valley.”