Fresh details have emerged over the proposed future use of the flagship HM Revenue and Customs office site in the city centre.
Cannon Capital Limited is seeking to convert the offices into 299 residential flats.
It has applied to the city council with a resubmission of an application to see if prior planning approval is required to change the use of the site to apartments.
The building went up for sale for £36m - and conservationists have recently applied to get the property Grade-II listed.
Hilary Silvester, executive chair of the Nottingham Civic Society, said: "An application for listing of the building has gone into Historic England - that was put in by the Civic Society.
"The architects have been consulted, they were involved.
"It was sent in by the Civic Society because it's architecturally innovative.
"Some of the things are very interesting, architecturally speaking, that is why it's been put in for listing.
"The point is that I think nobody objects probably to conversion but they would not want to see original innovative features, and design features, lost."
She said one thought that did occur to her was whether the building could be "suitable for educational use".
The Inland Revenue offices, designed by Michael Hopkins, were the first in the UK to achieve the BREEAM Excellent award and, in 1995, won the Brick Award for the best commercial and industrial building of the year.
This was followed in 1996 by a Concrete Society Certificate of Excellence and in 1997 the site was commended by a Civic Trust Energy Conservation Award.
"The city should keep such a building because of its architectural importance and technological importance," Ms Silvester said.
But she added: "It might be very difficult to incorporate the features that were specifically designed for that office building to incorporate them into residential, into apartments."
Ian Wells, vice-chair of the Nottingham Civic Society, spoke highly of the Inland Revenue building's innovativeness in incorporating environmental technology.
He said: "It's whole internal spaces incorporated precast ceilings - that type of thing, part of which was to help the ventilation of the building.
"It was predicated in creating a large building where that could be done."
He added that the building has to be of national importance to be considered for listing.
The iconic and quirky offices in Castle Meadows were for many years the headquarters for Inland Revenue, which had moved almost 2,000 jobs out of London to Nottingham back in 1989.
Its successor body, HM Revenue and Customs (HMRC), will soon be moving into the colossal Unity Square development near Nottingham Railway Station, leaving law firm Browne Jacobson LLP as the last remaining occupant.
Five of the six office buildings on the site were given planning consent in 2019, allowing for the change of use from offices to 332 residential apartments.
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