The ANC like so many other liberation movements that try to become political parties, believes it has the monopoly on morality and a divine right to rule.

The quest for absolute power makes internal conflict for positions of power inevitable and vicious, and the ruling cabal then seeks to eliminate challenges to its control from within and without. It begins to use the instruments of the Constitution, not only against the opposition, but against challenges it faces inside its own party.

That is what we are seeing now: power-hungry individuals pretending they exemplify the liberation struggle, and invoking it to justify the seizure of constitutional instruments that are actually supposed to limit their power.

What is the role of the opposition in this case? Our role is deceptively simple to describe but exceptionally difficult to fulfil. We must convince more and more South Africans that it is in their interests to protect the Constitution from the ruling party's abuse of power.

It is to persuade people that being in a demographic majority will not protect them from the consequences of power abuse by an increasingly small cabal that seeks to project its interests as the interests of a majority, and uses race mobilisation to disguise its real intentions.

Our role is to offer real policy alternatives that provide real opportunities for all who are prepared to use them to improve their lives, and where there is a link between effort and reward. It is to win elections where we can and to demonstrate our policies in action. 

We must be a catalyst that brings together all those who understand that limits on power are essential for the welfare of the people, so that South Africa can become a sustainable democracy with a growing economy.

In the medium term, as the consequences of the ANC's assault on the Constitution are felt more widely, the remarks I am making tonight will seem obvious. But unless we hear them and act on them now, it could be too late. This is why the DA's goal is to realign politics and re-shape the configuration of political parties, drawing a clear line between those who believe in constitutionalism and those who do not.

This realignment will not hinge on opposition parties alone, since it is not just opposition parties that care about the Constitution. There are many in the ANC who seek to defend the Constitution and who are appalled by the growing trend of anti-constitutionalism in their own party. But it will take them a long time to make the essential break because allegiance to a liberation movement becomes part of one's identity and the bonds are strong.

It is therefore vital to form a coalition of opposition parties which understands that we have a joint responsibility to defend the Constitution in order to offer hope to voters and bring them out in large numbers in next year's election. I and my party have been working hard behind the scenes to secure this outcome.

In truth, the response has been limited. One opposition leader remarked that such a coalition is a bad idea because we shouldn't gang up on the ANC. I was muted in my response to this statement because it is not appropriate for opposition parties, at this crucial juncture, to waste time and resources fighting each other.

But I thought, at minimum, I had to point out how truly ludicrous it is to suggest that an attempt to curb the power of a party that already has a 74% majority in Parliament amounts to "ganging up". This kind of response demonstrates to me that, despite all that has happened, some parties still have not fathomed what the role of opposition is in South Africa today.

I suspect that the real reason for this lukewarm response is that the leaders of individual parties do not wish to abdicate their own fiefdoms. After all, it is easier - and far less risky - to defend a dunghill than it is to move a mountain.

Whatever happens at the next election in 2009, we must strive to prevent the ANC from attaining a two-thirds majority because this is the essential minimum required to protect the Constitution, and prevent a shrinking cabal entrenching itself in power. If we can protect the Constitution, we will prevent South Africa from going down the well-trodden path of centralisation, cronyism, corruption and criminalisation that has been the lot of many failed states on our continent that could not make the transition from a liberation struggle to a stable constitutional democracy.

Apart from our role as opposition, we must also strive to demonstrate what we can do in government and show that our alternative is genuinely better, for all the people. We started this process by winning power in Cape Town in 2006 and in other local authorities, primarily in the Western Cape . We need to build on this base in 2009, by winning the Western Cape and showing what aligned co-operative governance can achieve between a provincial administration and local authorities. We are determined that people should experience what difference open, opportunity-driven governance makes in their lives. An opposition victory in at least one province will also help the ANC to get used to losing elections, so that we do not face the spectre of a Kenya or Zimbabwe, where the so-called liberation parties refused to accept defeat at the polls, and used political blackmail and threats of violence to stay in power. When that happens, it is clear that constitutional democracy has failed.

As Tony Leon put it in 1998 it is "one step at a time". If we achieve our goals in 2009, the next target is the local elections of 2011, when we must aim to win power, alone or in coalitions, in major metropolitan areas throughout South Africa. If we succeed in doing this, and if the chaos in the ANC predictably continues as the power-mongers continue their internal struggle with the constitutionalists, the stage will be set for a fundamental realignment of politics to bring together all those who understand that respect for the rule of law and the Constitution, is the only thing that stands between us and the prospect of implosion occurring in Zimbabwe today.

I have no doubt that, by that time, the disastrous consequences of Zuma's doctrine of the "higher law of the party" will be far more obvious to far more people and an ANC loss at the polls will be a realistic prospect.

The ANC can be dislodged from power. The Constitution can prevail. It depends on us. We can learn through our own bitter experience, or we can use the opportunity of learning from the experience of others, and apply the relevant lessons to our own situation. It is my role, and the role of my party, to ensure that there is no South African who can one day say: "I did not know. Why didn't anyone warn us?" We have to make the choices crystal clear. We are and we will keep on doing so. But then it is over to every citizen, to register as a voter, to go out on election day, and to make that crucial choice. After all, in a democracy, people get the government they deserve.

This is an edited extract from the C.R. Swart Memorial Lecture by Helen Zille, leader of the Democratic Alliance, delivered at the University of the Free State, August 28 2008