Helen Zille, the presidential candidate for South Africa's official opposition in next month's elections, has one chief obstacle. "I'm white," says the 63-year-old, "and there's nothing I can do about it. It's a bloody pity."

There it is, 20 years after the end of apartheid, an almost-inconceivable scenario: a white woman, an anti-apartheid activist from way back, insisting on her right to be viewed in a non-racial way, up against of the African National Congress's Jacob Zuma - a Zulu man with four wives (there were six but one died and one divorced him) who believes that having a shower after sex with an HIV-positive partner will prevent the spread of AIDS.

While Zille promises clean, efficient government, the $25 million government-funded "security upgrade" to Zuma's opulent family homestead, Nkandla (complete with a swimming pool, amphitheatre, cattle kraal and new houses for relocated relatives), has been deemed "highly improper" in a report by the Public Protector. Once a liberation movement, the ANC under Zuma is now riddled with corruption and cronyism.

At present, Zille's Democratic Alliance (DA) holds only the Western Cape province (taking in Cape Town), of which she has been the premier since 2009. She is hoping for about 30 per cent of the vote nationally and to win Gauteng province (home to Johannesburg and Pretoria). But it's hard, Zille tells Good Weekend, to compete against the ANC's "ground war", with its massive trucks and giant pantechnicons and fold-out stages that roll into villages with the promise of free sausages and T-shirts. For many people, these rallies are their only source of political information and they're being told by ANC speakers that, under the DA, apartheid will return - a prediction that, surveys show, 46 per cent of black South Africans believe. "When that [ANC] machine gets rolling, it gets people really worked up," says Zille.

In February, Zille tried to do away with what she calls the "race card" once and for all. In a flurry of hugs and kisses, she announced that a black woman, Dr Mamphela Ramphele, would become the DA's presidential candidate. A former World Bank director and once vice chancellor of the University of Cape Town, Ramphele had the perfect CV and "struggle credentials". The two women have an inextricably interwoven history dating back to the 1970s, when Zille earned her stripes as an investigative journalist for the Rand Daily Mail. It was Zille who broke the story of the torture and death of Ramphele's late partner, Black Consciousness leader Steve Biko, at the hands of apartheid police.

The ANC immediately dismissed Zille's alliance with Ramphele as a cheap "rent a black" tactic. Then it transpired that Ramphele hadn't properly consulted with her party, AgangSA, formed last year with the aim of providing an alternative for disenchanted ANC voters not prepared to vote for the DA, which is still predominantly white at the top despite a fast-growing black membership. There was a backlash, Ramphele reneged on the deal and the dream team collapsed in a humiliated heap. Zille's judgment was called into question.

When Good Weekend meets her in her city office a week later, she is still smarting. She courted Ramphele for three or four years, and this was a "betrayal of a different order" by someone she'd viewed as a personal friend. An embarrassing one, too: pictures of Zille and Ramphele's kiss sealing the deal were parodied mercilessly by ANC members, who promptly took to kissing each other on the lips at every photo opportunity.

"Listen, what's happened has taught me a very important lesson," Zille says. "I'm white. We're all equal before the law. I have an equal right to be here. And I have an equal right to do what I do. I'm not apologising any more for what I am." But had Ramphele's appointment worked out, she adds a little wistfully, not a person on the planet could have said the DA would bring back apartheid. "We would have killed that once and for all."

Apartheid is still the bogeyman, she knows. "People take it very, very seriously," says Zille. "People have such bitter memories of it. And those who don't remember it are absolutely terrified of it."

When Zille began speaking at the Nelson Mandela memorial service at Cape Town Stadium on December 11 last year, a ripple of booing broke out. In an instant, says a photographer who was standing nearby, the DA leader paused and took stock. She began, in a slightly embarrassing but touching fashion, to toyi-toyi (a kind of protest dance) and sing in Xhosa, her voice growing stronger and louder as she talked of the people of South Africa becoming one nation. "Viva, Madiba, viva!" she cried, her fist in the air.

The booing stopped, people joined in and, afterwards, says her spokesman Zak Mbhele, she went to sit with the red-bereted young men of one of the opposition parties, the left-wing Economic Freedom Front, led by young firebrand Julius Malema. If singing and dancing is what it takes, she'll do more of it, she once commented. "That's her style, disarming," says Mbhele. Opening a hospital in the sprawling black township of Khayelitsha in 2012, he says, she turned the podium around so that it was facing away from the dignitaries and spoke directly to the staff.

With her appearance too, she has made a huge effort. Friends who know her from the past say she is never more comfortable than when wearing a tracksuit, without any make-up. These days, Zille (who has a look of Margaret Thatcher about her, an unfortunate association, since Thatcher actively supported apartheid) projects what her personal assistant, Janine Schouw, describes as a "stately" look, modified for various events.

South Africa is at a tipping point, Zille believes. She has been counselled to take the long view, but says there isn't time. If things don't begin to change by the 2019 election, she says, it'll be too late, because many of the institutions of democracy - such as the National Prosecuting Authority (which prosecutes court cases on behalf of the state), the Judicial Service Commission (which makes recommendations to the president for judicial candidates) and even the Independent Electoral Commission - are under threat.

"If we wait too long, there won't be anything left to defend," she says. "These are critical moments. That's why we are growing new black leadership in the party as quickly as we can. Equally, we have to bring in experienced people, with struggle credentials especially, who can help us accelerate the process."

While reticent about her own "struggle credentials", Good Weekend learns that Zille hid ANC activists on the run from security police for extended periods during the states of emergency in the 1980s. Asked about this, she responds: "Why must I make a big deal of it? The people I hid know who they are."

Nomfundo Mpuntsha, a regional head of the South African Broadcasting Corporation until 2009, was an ANC student activist in the 1980s and detained for two years between 1985 and 1987. She is not one of those hidden by Zille, but says, "I'd vote for her as a white woman, me being an African lady. She's a bold woman, she's a hard worker." She likes that Zille speaks fluent Xhosa, one of the main local languages. But she didn't like the way Zille chose her provincial cabinet in 2009: "She had all white men and I thought, 'Uh-oh, I am sure she's making a mistake there.' "

Born in Johannesburg in 1951, Zille is the eldest child of Wolfgang and Mila Zille who had (separately) fled Nazi Germany in the 1930s: both her maternal grandfather and paternal grandmother were Jewish. Now, she's a member of the United Church. Her childhood was spent in Rivonia, today an affluent suburb of Johannesburg, but then "deep in the countryside". After the small local primary school attended "mostly by poor children", Zille says she found herself "definitely out of my comfort zone" in secondary school at St Mary's, a High Anglican church school.

She became a journalist but resigned in protest in 1981 after her editor at the Rand Daily Mail, Allister Sparks, was fired by its owners, the Anglo-American Corporation, because of his refusal to tone down the paper's "equal-rights rhetoric". While still a journalist in the '80s, Zille met her husband, sociology professor Johann Maree, and had two children, Paul and Thomas.

Zille started a public policy consultancy in 1989. Her move into politics flowed from an interest in education issues, and her role as chair of the governing body at her children's school. That led to an invitation from the then Democratic Party to draft its education policy. In 1998, she joined the DP (which in 2000 merged with other parties to become the DA) and in 1999, became cabinet member for education in the Western Cape legislature. In May 2007, she was elected party leader.

She believed, along with others, that a strong opposition was needed to keep the ANC in check. In 1994, already, Archbishop Desmond Tutu had memorably remarked that the ANC had "stopped the gravy train only long enough to get on". Zille was at the same time growing disenchanted with what she perceived as the party's shift away from Mandela's non-racialism. Then, in 1999, came news of the infamous $US4.8 billion arms deal, a military procurement package, which, says spokesman Mbhele, was the ANC's first opportunity for self-enrichment via state contracts and tenders. "It was the first temptation," he says, "and they succumbed."

The conflicts are inescapable and endless in a society where the subtext of the defence in the Oscar Pistorius murder trial is still widely recognised as "swart gevaar", which translates as "black danger" and refers to white people's fear of anonymous black intruders. Then there's the child rape, the gangsters, and the grinding poverty behind it all from which one cannot turn away. There are the ever-present difficulties of policing a country where, for example, people give a shack number for an address and by the time a line of questioning is followed up, the shack is gone.

Zille laughs at the suggestion that it is power that drives her in the face of such intractable problems. "I understand through my own personal background - my parents were refugees from Germany - that unless you get a political framework right, unless you have a constitution that protects people's rights to defend their own identity, there's no future for anyone in South Africa. We have a chance of getting it right. My mum did absolutely everything she could, from the moment she landed, to fight apartheid. She was absolutely appalled that she'd come from Nazism to apartheid. I saw how difficult it was for my parents to adjust ... I just always felt my destiny was here."

Has she ever been tempted to just leave? Go "packing for Perth", which has become the catch phrase for the departure of (mostly white) emigrants for Australia.

Zille puts her head in her hands, then looks up. "When I was about 31, I was going to marry and live in New York. About three months before the wedding, though, I realised I couldn't leave, so I broke off my engagement. It was hard to lose him but, frankly, it would have been harder to leave South Africa. I want this country to work. I believe it can work, and I want to be part of that. It's not some kind of selfless thing. It gives me a challenge every day - and purpose and meaning.

"Now I've got two children of my own. One son teaches maths in [the black township of] Khayelitsha and the other is an economics journalist for CBC South Africa. We're very grounded here."

Like the ruling ANC, the DA clearly backs free enterprise, but with some safety nets. Zille has education as her centrepiece and wants to use welfare measures to address the worst poverty, while the ANC is said to be still tussling within its ranks over moves that would return it to a more socialist path.

To date, the ANC's Black Economic Empowerment (BEE) policy is mostly credited with having produced a class of black millionaires and multimillionaires, usually as a result of share options from board positions with big corporations. BEE, argues Zille, has managed only to "over-empower" a small, well-connected elite.

Instead, she talks about steady aims: partnerships with smaller, black-led business enterprises; job creation through a youth-wage subsidy; internships and "incentivised" education, with opportunity vouchers and bursaries for able, keen students in need.

Her party's trump card is President Zuma, his excesses and indiscretions. The country is still in uproar over the grandiosity of Nkandla, and then there is last year's "Guptagate", where a private flight from India bringing 200 guests to the wedding of Vega Gupta, the son of a tremendously wealthy ANC supporter, was allowed to land at a military base where guests reportedly skipped customs regulations - with Zuma's blessing.

In February, Zuma's son Edward was accused by the South African Revenue Service of trading in contraband cigarettes and hiding millions in profits. "The poison of corruption seeps into everything, from tenders for school lunches to the fluffed pillow of the presidential palace," said one commentator recently.

Zille, by contrast, tells Good Weekend she is "the poorest" party political leader in South Africa, despite the "ANC narrative" that "she's there to further the economic interests of rich white people". "I've got no business interests," she says. "I've got a little house I bought a long time ago, in 1984, next to the railway line. I've never lived in a white group area, except when I was very young, and now, in the Premier's residence. I was always in a small minority of whites where I lived."

The DA's fastest growing constituency, Zille says, is black people, and not necessarily the well-connected middle class, many of whom have benefited from the ANC's preferential treatment. Zille says black support in the Western Cape, where she is premier, is now coming from the township of Khayelitsha. In the Eastern Cape, the country's poorest province (where Nkandla is situated) her base is, she says, "nothing short of phenomenal". Within the party, black, coloured (mixed race) and Indian people now outnumber whites.

And yet Zille knows the DA cannot win this May 7 election, which she says is why she offered herself as candidate following the Mamphela Ramphele fiasco. "Let me be second best to Mamphela this time," she says, of the possibility that the DA's accomplished 33-year-old parliamentary leader, Lindiwe Mazibuko, could stand in 2019 when her chances are higher.

In the world of South African race politics, Mazibuko is labelled the "tea girl" to Zille's "madam" by the ANC, and "not black enough" because her private-school accent "sounds white". Yet in parliament, Mazibuko is feisty and articulate, defying the cultural baggage attached to a young woman challenging an older man like Zuma on everything from policy to personal morality.

In the Cape, Zille says her party delivers, citing good news on school retention rates (up from 36.9 percent in 2009 to 52.1 percent in 2013) and public health (it has the lowest HIV mother-to-child transmission rate and the highest condom distribution rate in South Africa). Nevertheless, Cape Town has its share of "service delivery protests" - a euphemism for the large, angry, protest marches that dog the country. On a wall in front of a township along the airport freeway is emblazoned the graffiti "Cape Town works for some", a parody of the Town Hall's slogan: "Cape Town works for you." And there is another threat to Zille's world view. Fast gaining traction is Julius Malema's Economic Freedom Fighters party and its policies that include nationalisation of the mines and compulsory land and wealth redistribution.

On the divisive subject of affirmative action, the ANC has quotas based on race, while the DA favours disadvantage as a decider. Race-based programs, the DA holds, buy into apartheid's race classification system, which had separate categories of privilege for whites, Indians, coloureds and blacks.

The ANC's policy, Zille says, prohibited the promotion of an "excellent" Indian policewoman, JeMilla Naidoo, in 2013. Indian women, she explains, constitute only 0.037 of the police force employment equity target, which gets rounded down to zero, making it impossible under the formula for an Indian woman to be promoted beyond major in the police force. "If you don't fit a certain racial profile, you don't have a chance," she argues. "It's mad. Demography as destiny."

Instead, DA policy relies on the idea that race and disadvantage are profoundly linked. Of the 800 or so young interns Zille has employed for the city, 95 per cent are black - but the disadvantage test, she points out, does not exclude anyone else.

Prominent journalist and author Donwald Pressly says Zille may be becoming an icon across cultural groups: she turns up in traditional Xhosa gear and ululates and "does the whole cultural thing". She's not lost her party any Afrikaner support, she appeals to the coloured minority "in a big way" and, as the only white politician trusted in some black communities, has managed to draw in new black support for the DA.

Pressly refers to her leading an almost entirely black march for youth wage subsidies in 2012 in the Johannesburg CBD. "She understands the defeat of unemployment, and working-class and middle-class concerns - and rich concerns. If anyone is going to sell free-market economics, it will be her."

But in a country desperate for an alternative, there are still people who cannot bring themselves to vote for Zille - or the DA. They may not vote at all. For them, Zille reserves her most acid comment: "I often say to people, you will never find a perfect political party and if no political party is good enough for you, then why don't you start one yourself and try to get people beyond your immediate family to vote for you?"