The National Archives are ill-equipped to deal with the deluge of declassified information likely to ensue once the Protection of Information Bill becomes law, the Nelson Mandela Foundation warned on Wednesday.

"We have reservations as to whether the archives is the appropriate state body to take on this responsibility. The national archives are desperately under-resourced," Vernon Harris from the foundation told the ad hoc committee drafting the contentious bill.

Harris recalled that the Truth and Reconciliation Commission archives had yet to be catalogued by the National Archives though the commission's print files were transferred there in 1999.

With over-classification believed to have been the norm since the Minimum Information Security Standards became policy in 1996, MPs have been grappling with the question of what to do with secret files from the recent past as well as the apartheid era.

According to the bill, information may not be classified for more than 20 years unless the head of the state body that filed it as secret certifies that continued classification is necessary for the national security.

Lawmakers have agreed that once the new law is passed, all state departments will be compelled to launch a review of their classified records, whether they date back 20 years or less, raising the spectre of a large scale review of secret files from the apartheid years through the Mandela and Mbeki eras.

If the state department no longer exists, the task will fall to the intelligence agencies.

But Democratic Alliance MP David Maynier said this created the risk that information like the apartheid regime's files on state informers during the liberation struggle could be abused to settle scores in the ruling party.

"The really hard case is the informer files of BOSS etc... they could use that information to settle scores, particularly within the ruling party."

Maynier has argued that a neutral body should be given care of information classified in the past, and said if nobody had the budget to take on the responsibility, costing should be done and funding found.

His comment on factional battles drew scorn from ANC MPs, and Harris pointed out that experience had proven that the intelligence and police departments were among the most forthcoming state departments when asked to release documents under the Promotion of Access to Information Act.

"The most co-operative state institutions, were the security establishments," he told MPs, adding that those further removed from the issues and therefore less informed were "insecure" about releasing information.

Harris questioned the wisdom of proposals that information that had been classified for 20 years or more should be automatically declassified.

He recounted that he had been tasked to go through former president Nelson Mandela's private correspondence and argued that though most of it dated back more than two decades, it could not summarily be made public if it concerned intimate details about a third party.

Inkatha Freedom Party MP Mario Oriani-Ambrosini disagreed, saying Mandela was one of history's great figures and as with Winston Churchill and John F Kennedy, public interest argued for the release of all information.

MPs are expected to turn on Thursday to the question of how to define national security as a cause for classifying information. The issue has raised heated debate and the ANC is expected to argue that the bill should not seek to define the notion, leaving it up to the courts to interpret its meaning.

This is likely to be rejected by opposition MPs, who are in the minority on the committee drafting what has so far been the most divisive bill of the post-apartheid era.

The deadline to conclude the legislation is September 23.