Sections of the government's proposed Protection of Information legislation are reminiscent of apartheid-era secrecy laws, according to an intelligence expert.

They also displayed a fundamental misunderstanding of the Constitution, Dr Laurie Nathan said in a submission to Parliament's ad hoc committee on the Protection of Information Bill.

Nathan was a member of the Ministerial Review Commission on Intelligence, which ran from 2006 to 2008; the Parliamentary committee is holding public hearings this week on the bill.

Nathan said that while there were legitimate grounds for protecting certain information, this should be the exception and not routine.

"The government cannot seek to avoid all possible harm that might arise from the disclosure of sensitive information," he said.

"Some risk of harm has to be tolerated in a democracy because the dangers posed by secrecy - lack of accountability, abuse of power, infringements of human rights and a culture of impunity - can imperil the democratic order itself."

Nathan said that sections 11 and 15 of the bill, which provided for classification of sensitive material and defined "the national interest" very broadly, were its most problematic.

"They provide so general and sweeping a basis for non-disclosure of information that they are reminiscent of apartheid-era secrecy legislation... and in conflict with the constitutional right of access to information," he said.

They also clashed with the Promotion of Access to Information Act.

Nathan said that the definitions would be extremely difficult to apply in practice.

Officials in all organs of State would have to decide whether disclosure of particular information might harm "any matter relating to the advancement of the public good" or the "pursuit of justice, democracy, economic growth, free trade, a stable monetary system and sound international relations".

These phrases were capable of many interpretations and there would inevitably be significant inconsistencies between the classifications made by different officials.

Because the definitions of "national interest" and "national security" were so broad, they were likely to lead to a "chronic over-classification of state information", reminiscent of the apartheid era.

The two sections flowed from the belief set out in the bill that "secrecy exists to protect the national interest".

"This line of thinking is constitutionally unsound," Nathan said.

"Since the 'national interest' includes the pursuit of justice and democracy, as stated in section 11, it is not secrecy but rather transparency and access to information that protect the national interest."

He said that the bill suggested that the Constitution's provisions on openness and access to information were "subject to the security of the republic, in that the national security of the republic may not be compromised".

"This is also a fundamental misunderstanding of the Constitution, whose approach to security requires openness and access to information," he said.

Secrecy should instead be motivated with reference to "specified and significant" harm that might arise from the disclosure of particular information.