It’s the battle over one of the best-known landmarks in the capital and opponents of the plan to make it home to a super-luxury hotel hope the last nail is about to be hammered into its Rosewood coffin.

Scottish Natural Heritage has now followed Historic Scotland with an apparently stinging criticism of the plan by Urbanist Hotels and Duddingston House Properties (DHP) to turn the old Royal High School on Calton Hill into the latest link in the Rosewood hotel chain, but the coup de grace could be the formal application from the rival bid to re-open it as a school.

The plan to transfer St Mary’s Music School from the West End is at an advanced stage and the team led by developer Willie Gray Muir aims to submit its designs to Edinburgh City Council within the next three weeks.

The design team believe the new buildings needed for classrooms and boarding facilities will actually be lower than the existing derelict gymnasium block to the east of the site.

What has yet to be revealed is that the Music School concept involves cutting a new entrance into the plinth beneath the famously austere frontage overlooking Regent Road, something which was removed from the hotel design after public consultation.

But from private communications I’ve seen, the St Mary’s consortium is brimming with confidence that their plan will glide through the planning process with universal acclaim.

They have already met with the Edinburgh Urban Design Panel (EUDP) and claimed their reception was little short of euphoric. Given the EUDP was established by the city council and is chaired by its head of planning, David Leslie, no wonder they were happy.

Now the music school team is determined to get their plans into the minds of the planning councillors before December 17 when they are set to make the decision about the “Inca temple” hotel design by award-winning architect Gareth Hoskins.

The presumption is that getting the music school plan into the open will mean public opinion, and therefore councillors’ attitudes, will be swayed by more detailed knowledge of what is already being billed as the “perfect” plan to breathe new life into the rotting Georgian Greek revival pile.

However, close observers of Edinburgh’s planning decisions believe there is now not much swaying to be done, with the tone of the planning committee changing markedly since the departure of economic development chief Frank Ross.

Recent decisions to block a care-home plan on rough ground at Meggetland and a small housing development on a disused private school playing field point to a significant change of attitude to the group which approved a controversial housing estate at the former mental hospital at Craighouse.

So threats of the loss of the New and Old Towns’ World Heritage status will not matter if, as now seems likely, the committee simply hates the hotel idea and loves the school.

However, the remaining process is not supposed to be a choice between two schemes – the council lost that option by signing the agreement with DHP – but only whether the hotel plan is acceptable or not.

Its rejection will come with a high price tag for the cash-strapped city because a costly legal war is almost certain to ensue – DHP boss Bruce Hare has already promised as much – and it will be years before the music school flit can be completed. In the meantime the council will be saddled with an annual maintenance bill running to hundreds of thousands of pounds.

The hotel team claim public opinion outwith the New Town backs their plan and a key ally is Marketing Edinburgh chief executive John Donnelly who identified the need for a globally-recognised luxury operator like Rosewood in the international travel markets. Not without justification, he pointed out that a new home for a private music school wasn’t exactly high on Edinburgh’s priorities.

That was a view shared by senior SNP councillors like Mr Ross with economic development at the top of their agenda, and although commercial interests have trumped planning concerns in recent decisions like the new St James Centre, the pendulum is swinging the other way.

The recent halt called on the £400 million Buchanan Street Galleries expansion is evidence of the continued fragility of property investment in Scotland, and the worry in Edinburgh’s pro-development circles is that snubbing a prized operator like Rosewood will send a poor signal about the city’s desire to compete.

The Old Royal High symbolises the tension between preserving the past and building a prosperous future but does turning a landmark into an institution for a tiny musical elite strike the right balance? I’m not so sure.