Backed by the philanthropic Dunard Fund, the Trust’s vision will provide an alternative to Hoskins Architects’ £75m plans to turn the school into a hotel.

Richard Murphy Architects and Simpson & Brown were appointed to develop alternate proposals for the restoration in September.

Their plans will see a 300 seat concert hall and the creation of three new public performance spaces and a contemporary foyer providing space for ticketing, bar and cloakrooms that will also double up as a multi-functional space.

A new public entrance, terraces and ‘near invisible’ new build elements are also envisaged.

William Gray Muir, chairman of The Royal High School Preservation Trust, said: “We fully recognise that the City of Edinburgh Council is not currently in a position to accept our offer due to its existing commitment to a commercial development. However, we have consulted widely and believe that our plans satisfy the need for conservation, public access, a culturally suitable and economically sustainable use.

“Therefore, if the commercial application were refused, the Trust is poised and ready to enter any new competitive process to acquire the building for St Mary’s Music School. Such a process could be completed in a matter of months.”

The City of Edinburgh Council already has an agreement with developers Duddingston House Properties meaning the music school proposal is only likely to continue if councillors on the planning committee first reject the hotel plan.

Planners have yet to decide whether to give the green light to the hotel scheme.