A Conservative MP is calling on the information commissioner to overrule government attempts to keep the sites of Titan prisons under wraps.
John Baron's original freedom of information request asking for the sites to be specified was rejected by the government.
"Ministers want to buy the land for a Titan prison without even telling local residents," Mr Baron said.
"Any consultation which takes place after land has been bought is bound to be a sham, because communities will be presented with a done deal."
The proposed prisons, which have virtually no support among penal experts, will house around 2,500 convicts.
A letter from justice minister David Hanson confirmed plans for one prison in the Thames Corridor, but refused to list further plans for fear of "prejudicing the commercial interests of the government.
A second letter from Shahid Malik MP confirmed ministers wanted to retain the option of buying land before announcing their plans for a jail or undertaking a consultation.