The national heritage watchdog has criticised plans for a hotel at the former Royal High School in Edinburgh.

Historic Scotland said in a letter to planners that Thomas Hamilton's masterpiece on top of Calton Hill would be overwhelmed by plans to build round the nineteenth century neoclassical main building.

The body wrote: "We believe the proposed hotel development, in particular the redevelopment of the western playground, would have a significant adverse impact on the setting of the Category A listed former Royal High School, including views to and from the main building and associated structures - pavilions, screen walls, gateways and railings - which all contribute to the present integrity of the original concept.

"The proposed extensions to the listed building, by their height, scale and massing, would clearly dominate and overwhelm the listed building, challenging its primacy on the site and diminishing significantly the building’s status as an internationally-acclaimed exemplar of Greek Revival architecture."

The £75 million plan to convert the empty building into a hotel is led by Duddingston House Properties and Urbanist Hotels.

David Orr, co-founder and chairman of developer Urbanist Hotels, said: “Historic Scotland was part of the Architecture and Design Scotland forum - set up by the Scottish Government to promote the value of good architecture and sustainable places - which discussed the project in detail during three workshops between February and May 2015.

"This resulted in A&DS not only supporting the proposal but commending it as well-considered."

He added: "We remain focussed on the complete restoration of Thomas Hamilton's masterpiece and are proud of the designs for the new additions to the site, the quality of which has been commended as architecture of a very high calibre.

“By creating a world-class new accessible destination for Edinburgh locals and visitors alike in partnership with an impeccable brand like Rosewood (Hotels group) we will be able to create hundreds of high-quality jobs and showcase our beautiful capital city and Scotland’s creative and cultural talents to a new global audience.”

Edinburgh City Council granted DHP a 125-year lease after the company won an open competition in 2010.