In the letter to Westbury Region Against the Prison president Linda Poulton, obtained by The Examiner, Ms Archer said during the site assessment process "the land nominated at Westbury was deemed to be by far the most suitable, with all other sites having significant deficiencies".

Ms Poulton said she was concerned the government had made up its mind on the site before consultation was finished.

"It certainly seems that, if it's true that these other sites have significant deficiencies, she is suggesting Westbury is being zeroed in on as the only site," Ms Poulton said.

"Combined with the drilling on site the other day it's looking increasingly likely they are very serious about this site.

"The fact they have fixated on Westbury is something we've been worried about for day one but that doesn't shake our resolve."

Lyons Labor MHA Jen Butler said there was a lot of evidence to suggest Westbury was always the only site being considered.

"[This correspondence] states that Westbury pretty much is the only site," Ms Butler said.

"There's been so much secrecy. There's been a lack of information. We know that work has already started on that site."

Ms Archer reiterated on Sunday no final decision had been made regarding the prison's location.

"The Tasmanian government has committed to an extensive consultation process with the Westbury community on the preferred site for the Northern Regional Prison," Ms Archer said.

"SGS Economics are independently undertaking a Social and Economic Impact Study, including direct contact with residents, as I previously confirmed in December 2019.

"I have previously indicated to the Westbury community that interim results from the study would be shared with the community in February."