The Department of Immigration has been slammed for a planned $255 million office fit-out.

The department is seeking approval for one of the most expensive plans of its type in federal government history, fitting out a new Canberra headquarters to reduce the number of buildings the department inhabits from 12 to five.

The project would place the department’s main office in a new state-of-the-art building next to Canberra Airport.

But the plans have kicked up a litany of criticism, with the politicians in charge of approving the works accusing the department of poor preparation and a lack of transparency.

Members of the Parliamentary Standing Committee on Public Works castigated the Department of Immigration and Border Protection (DIBP) for providing incorrect figures in a hearing last week.

DIBP secretary Mike Pezzullo said the numbers came from a consultant who used “the wrong spreadsheet”. 

Pezzullo went on to claim that the consolidation would bring a net saving to the taxpayer of about $230 million over 30 years.

But the committee members questioned the cost claims, saying they relied heavily on landlord “lease incentives”, which could distort the true cost of the proposal.

“The committee is deeply unimpressed with the way it has been provided with information on this project to date,” Liberal committee chairman Scott Buchholz said.

He accused the department of repeatedly changing its proposal without giving new information.

“This is unacceptable as the committee can only make judgements about the project based on the information that is provided.

“While I do not believe it is the department's intention to be uncooperative, it would be understandable if the committee members saw the department as unco-operative witnesses,” Buchholz said.

Labor senator Alex Gallacher said the building has been largely empty for the last eight years.

“You're paying the maximum rate that you would pay for a lease in Canberra, in an area where the building is eight years old and there is allegedly somewhere between a 20 per cent and 40 per cent occupancy rate,” he said.

Senior department official Ben Wright maintains that it is a “good deal”, because the building's “cold shell” status makes it cheaper and easier to fit out.

Works should begin in August, and be completed by February 2021.