The secret document that decided Belconnen's future

Despite the intense public and commercial interest around the future of Immigration in the northern town centre, the department is determined to maintain a cloak of secrecy over the report, claiming it is "commercial in confidence".

The Finance Department is using the same justification to keep the public in the dark about details of its own upcoming move to high-end accommodation in Canberra's leafy inner-south, which will cost taxpayers hundreds of millions of dollars over the lifetime of the lease.

Finance Minister Mathias Cormann has backed his department's stance to keep the Belconnen information from taxpayers, who paid $27,000 for it to be compiled by accounting giant Deloitte.

But Finance is set to come under pressure to release the information when its bosses appears before a Senate Estimates Committee next week as ACT Labor politicians push for it to be made public.

Much of Canberra's commercial property sector was left fuming last month when the Finance Department announced it was cancelling the tender to provide new offices for DIBP.

Several local and national property outfits, which each spent hundreds of thousands of dollars putting bids together for deal, have had to say goodbye to their money as a result of the decision.

The same players were left out of pocket a year ago when a requirement for a new building for the Customs agency was abandoned after the announcement that Customs would merge with Immigration and form the Australian Border Force.

The decision came after more than 12 months of lobbying and jockeying for position among powerful property interests keen on securing the signature of the large government tenants.

Senator Cormann agreed to the local impact requirement after lobbying by the ACT's federal politicians, most notably Liberal senator Zed Seselja.

Commonwealth property acquisition rules have also been changed to include a local impact test and requiring the minister to sign off on any deals worth more than $30 million.

Fraser MP Andrew Leigh said the refusal to release the report could reflect a desire to keep Canberra residents in the dark.

"Is the government hiding this local impact assessment because they don't want Canberrans to know the very real economic harm caused by shrinking or moving our public service agencies?" Dr Leigh asked.

"This decision comes as they are planning the pointless move of up to 600 public servants to Gosford to work in a white elephant office block.

"Finance should release this local impact assessment now so we can see exactly how much public service agencies contribute to Canberra's local economies."

A spokeswoman for Senator Seselja said the former Canberra Liberals leader understood why the public was not to be allowed access to the document.

"Senator Seselja understands the decision made by the Department of Finance," the spokeswoman said.

"He understands legal advice has recommended the report not be released due to being commercial in confidence.

"What is important is that local impacts were considered and the Department of Immigration will continue to have an office presence in Belconnen.

"This is a great outcome for the town centre, local businesses, staff and residents."