The national heritage watchdog condemned proposed extensions that are central to the redevelopment, saying the wings will “dominate and overwhelm” the 200-year-old listed building.

Developers Duddingston House Properties submitted revised plans for the project earlier this month after a public consultation “fundamentally altered” the initial plans.

A proposed design for a 160-room development released in March was criticised from heritage groups for being too modern and not blending into the surrounding area.

Architect Gareth Hoskins said the new 147-room proposals will create a “new, world-class hotel”, which is expected to create 260 jobs.

However, the official objection from Historic Scotland means Scottish Government Ministers will be able to “call in” the application and order a public inquiry even if the plan is approved by the City of Edinburgh Council.

In a letter of objection to city council planners, the heritage agency said 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 letter states: “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.”

Fears were raised over the effect on natural features and historic landmarks such as the National Monument and the nearby art deco headquarters of the Scottish Government.

It adds: “The proposals would impact on the key characteristics and landscape features of the hill, as well as the carefully-planned setting and relationship between the hill and the former school, the latter having been thoughtfully designed and positioned to harmonise with the natural contours of the site.

“In turn, the development would impact too on the monuments on the hill and their important relationship with the former school and on other adjacent category A listed buildings including St Andrew’s House.”

Work is due to begin next January, with the hotel scheduled to open in March 2018.