Developers bidding to turn one of Edinburgh’s most famous landmarks into a hotel have hired a former adviser to Donald Trump as the battle over the empty architectural masterpiece intensifies.

The hotel consortium vying to secure the Old Royal High School project has appointed the legal expert who helped the US President win approval for his Aberdeenshire golf course.

Ann Faulds, a partner with CMS and head of planning and transport at the law firm, headed up Mr Trump's legal team during his controversial development at Balmedie.

She also previously advised the then Scottish Executive on its policies for compulsory purchases of land for development.

Her appointment comes as it emerged that Urbanist Hotels and Duddingston House Properties have filed an appeal after councillors rejected its revised plans to build a smaller “six star” hotel around the A-listed neoclassical building for about £75 million.

The consortium had already had its earlier plan, for a larger hotel based on two multi-storey wings, rejected.

The Scottish Government has now said that its planning officials could study both projects in tandem in a public planning inquiry.

A spokeswoman said all four appeals by the developers, which included two appeals over the council’s refusal to give listed buildings consent, would be “conjoined”.

She told the Guardian: “Each of the four appeals will be decided on their own merits.”

But those behind a rival £35 million bid to relocate St Mary's Music School across the city to the Old Royal High have criticised the move.

William Gray Muir, chairman of the Royal High School Preservation Trust, said a planning inquiry with such a broad remit would “end up in total confusion”.

He added: “It is absolutely clear that both applications substantially fail the statutory test for what is acceptable for a protected building.”

Historic Environment Scotland, the government agency, said it had formally objected to the hotel plans and would take part in a planning inquiry.

Officials from the Edinburgh World Heritage Trust have also voiced concern about the hotel proposal, amid fears it would threaten the city's protected status as a UN world heritage site.

Adam Wilkinson, director of the trust, said: “Plonking two very large hotel wings on either side of a classic building in a classical landscape setting removes a lot of meaning from the site.”

But David Orr, of Urbanist Hotels, said the firm was “committed to reviving a building which has failed to have a credible and sustainable use for nearly 50 years”.

He said: “Our proposals guarantee the future of Hamilton’s masterpiece, both architecturally and financially, and we feel that the appeals process will allow many of the complex technical issues raised with both previous planning applications to be thoroughly presented and cross-examined.”