Developer Trevor Osborne, the man behind the transformation of Oxford Castle, says his company is not the one selected to revamp Abingdon's Old Gaol.
The Vale of White Horse District Council will only confirm that it has selected a "winner" from an undisclosed number of short-listed bidders.
But Mr Osborne said his plans for a hotel and heritage complex at the Old Gaol had been rejected.
And he hit out at the council's "extraordinary" handling of the selection process.
The district council, which owns the building, has agreed to consult both the town council and the pressure group, Community in the Old Goal (Cog), about the new development. But they must sign a confidentiality agreement that forbids them from making any information public.
The concessionary move follows growing pressure on the Vale to release the winning developer's name and details of its scheme.
Mr Osborne said: "It seems a denial of democratic access to information. They don't want to tell people who is the preferred bidder or what the scheme is. I have never known anything like this.
"It's quite extraordinary."
He had hoped to follow up the successful £40m Oxford Castle development, which received 12 architectural and heritage awards, by taking on the 200-year-old Abingdon site.
Mr Osborne said: "It's disappointing. I can't imagine what would bring in more vitality than what we were proposing."
Cog secretary Hester Hand said: "We're considering our options, because we think this offer has a lot of pitfalls.
"It would mean that our representatives would be barred from discussing issues with our own members."
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