Immigration bosses have been lambasted over their plan to spend a quarter of a billion dollars fitting out a new office, with the politicians asked to approve the proposal accusing them of poor preparation and failing to provide vital information.

Even Turnbull government MPs say they are "deeply unimpressed" with the Department of Immigration and Border Protection's handling of the mega-proposal, going so far as to compare its top officials to "unco-operative witnesses".

In a heated hearing last week, members of the Parliamentary Standing Committee on Public Works also castigated the department for providing it with incorrect figures, a blunder secretary Mike Pezzullo blamed on a consultant who used "the wrong spreadsheet".

The department is seeking approval to spend $255 million to fit out a new Canberra headquarters, in what is thought to be the most expensive plan of its type in federal government history. Under the proposal, the number of buildings the department inhabits in the national capital would shrink from 12 to five, with the main office located in a new state-of-the-art building next to Canberra Airport.