Though the American founding fathers disagreed when they opted for the separation of powers, the finest system of government ever devised is the Westminster model.

Its distinguishing feature is that the executive is responsible to parliament. This is marvellously paradoxical, making parliament both supine and supreme. For most of the time, party discipline ensures that members of parliament (MPs) do as they are told, so the executive branch of government is invariably safe. Occasionally, however, when parliamentarians revolt, the results are democratically splendid: prime ministers replete with power one minute can find themselves out of office the next.

The most famous such incident was in the House of Commons in May 1940 when a backbench Conservative revolt against Neville Chamberlain's poor performance as war leader paved the way for Winston Churchill to replace him as prime minister.

Our old constitution was based on that of Westminster, and here too the war cost a prime minister his job. Though coalition government made circumstances different, Gen James Hertzog had to resign the premiership to Gen Jan Smuts in 1939, when Parliament voted with Smuts for war with Germany and against Hertzog's neutrality proposal.

Our present constitution is partly built on the separation of powers between Parliament, executive, and judiciary. But it also retains the key Westminster feature making the executive ultimately subordinate to Parliament.

A parliamentary revolt against government's handling of HIV/ AIDS is to be desired, but too much to hope for. Parliament can nevertheless do plenty to rebuild the authority it has lost.

This will not happen if left to the caucus of the ruling party, which proposed merely to "censure" Tony Yengeni for lying to Parliament about his vehicle. This is not the behaviour of parliamentarians who take the institution seriously.

A great deal therefore depends upon the Speaker, Frene Ginwala, who broke ranks with other African National Congress (ANC) MPs over Yengeni and demanded his resignation. She also recently criticised various ministers for playing "fast and loose" with Parliament.

If ministers treat Parliament with disdain, however, the institution has itself to blame. Ginwala shares that blame. She failed to defend the standing committee on public accounts two years ago when her party torpedoed its investigation into the cabinet's arms purchases.

According to Gavin Woods, who later resigned chairmanship of the committee in frustration, Ginwala was among those who "blocked" the investigation. Moreover, Yengeni did more damage to Parliament by helping to sabotage the committee he axed the nonservile Andrew Feinstein as its ranking ANC member when he was ANC chief whip than by subsequently lying to it.

Parliament does not have to rely solely on its own skills to hold the executive to account. The constitution establishes other "institutions supporting constitutional democracy", among them the auditor-general and the public protector, who are accountable not to the executive but to Parliament.

In a case brought by one of the losing arms bidders, these two officials, along with the national director of public prosecutions, were ordered by the Pretoria High Court last year to hand over various documents relating to the arms deal. They have been granted leave to appeal on the grounds that they do not have the resources to identify the documents.

Not enough resources to identify documents relating to a transaction for which Parliament has merrily voted to spend R59bn ? Clearly, the malaise corroding Parliament has spread to some of its watchdogs.

Ginwala faces a mountainous challenge if she wishes to reassert Parliament's authority. Its predecessor became an instrument of the National Party government.

History should not be allowed to repeat itself. One day, ANC backbenchers may be called upon to stop government from playing fast and loose with HIV/AIDS.

Kane-Berman is CE of the SA Institute of Race Relations.

With acknowledgements to John Kane-Berman and Business Day.