Plans for a £40 million hotel in the heart of Edinburgh's Old Town have been attacked for destroying the “rhythm and elegance” of the city centre by the novelist Alexander McCall Smith and Sir Timothy Clifford, the former director general of the National Galleries of Scotland.

In a letter to The Times, Mr McCall Smith and Sir Timothy join six other eminent figures in deriding the plans for SoCo, a hotel which has been designed to rise from the Cowgate on to South Bridge in Edinburgh, on a site destroyed by fire in 2002.

The authors of the letter - including Alexander Stoddart, the sculptor, Douglas Rae, the film producer, and Professor Richard Demarco - describe the aftermath of the fire as the perfect opportunity to restore the symmetry of South Bridge, which was planned by Scotland's pre-eminent architect, Robert Adam, but completed by Robert Kay, in 1786.

The authors argue that an opportunity has been tossed away in a proposed development that only pays the most “grudging respect” for Adam's designs, offering instead “yet another dose of the sort of international modernism which should have no place in Edinburgh's fragile Old Town”.

Recently the SoCo project, which proposes a 200-room hotel alongside other commercial developments, has been criticised by the Architectural Heritage Society of Scotland and the Cockburn Association, for failing to match Edinburgh City Council's original expectations for the site.

John Shepherd, managing director of Whiteburn, the company developing SoCo, however, dismissed the criticism and said that the original 18th-century scheme for South Bridge had never been implemented properly because of lack of finance. Adam would have been “very proud of what we are doing,” he added.

“What was built by Robert Kay was not Adam's design and was not fit for purpose. If the Adam scheme had been built, then South Bridge would not be suffering the dereliction it does now,” Mr Shepherd said.

In its 2003 planning brief, Edinburgh City Council noted the historic importance of South Bridge as “the first example in the city of a whole street built to unified facade design”.

The council insisted that any redevelopment must recognise the sensitivity of the site, within the established World Heritage area which extends over the Old and New Towns.

Mr McCall Smith and his colleagues lambasted the design advanced by the developers and said it failed to address Adam's masterplan, adding that the “development currently under consideration will destroy the integrity of one of the great monuments of the classical world”.

“The developers intend to replace the lost corner of Adam's masterpiece with a hotel which on the Cowgate elevation pays only the most grudging respect to Adams gable ends, and which on the bridge's pays absolutely none at all,” they wrote.

Mr Shepherd said that his company had followed the city council's planning brief to the letter, and it had not called for either Kay's or Adam's scheme. “What we have designed is an innovative and bold scheme which does respect the architectural heritage of the area and will produce something that will provide accommodation for visitors, jobs, and above all life, breathing something back into what are at the moment very derelict streets,” he said.

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