Senior bureaucrats threatened to stop giving honest advice to the Federal Treasurer if negative gearing documents were not kept secret from the ABC.

Treasury public servants fought for almost two years to stop the release of information that showed the predicted impact of Labor's negative gearing policies.

They argued that disclosure of the information would prejudice Treasury's "ability to provide candid and confidential advice to ministers in the future".

Public servants often argue that if their full and frank advice to politicians about policies is released, this will damage the relationship with ministers, and releasing documents is therefore against the public interest.

However the ABC was successful in its appeal to the Office of the Australian Information Commissioner and Treasury accepted the independent umpire's decision the negative gearing information should be released.

"The general public interest is high because of the enormous, ongoing annual cost to the federal budget", the ABC successfully argued.

"In an environment where taxes on financial institutions and taxpayers are rising (via a proposed bank tax and Medicare levy hike), disclosure of these documents would increase oversight of the Government's decision not to change these concessions."

Freedom of Information guidelines state that public servants are obliged to provide robust and frank advice at all times, and that obligation will not be diminished by transparency of government activities.

The ABC late yesterday sent questions to department boss John Fraser but a spokeswoman said: "Treasury does not have any further comments to add."