Twenty years ago, while social activist Medha Patkar was protesting against US energy firm Enron's Dabhol Power Station, which was being set up 160 km south of Mumbai along the western coast, Meera Sanyal, as head of the Indian arm of a foreign bank, was helping to finance the project.

At that time, Enron's stake in the gas-based coastal power plant was the largest foreign investment in India. The US firm later went bankrupt after being charged with accounting fraud, but in 1994 it was still the darling of Wall Street. Many prominent Indians were calling the power plant a test case for India's new policy of economic liberalisation.

In this charged atmosphere, social activist Patkar and high-flying banker Sanyal stood on diametrically opposite sides. On the face of it, they represented two fundamentally different models of economic development.

Yet today, Sanyal, 52, and Patkar, 59, find themselves sharing a platform  – of the Aam Aadmi Party, which has chosen them as candidates from Mumbai for the forthcoming general election.

Sanyal will contest from south Mumbai, a precinct with a huge concentration of some of the country's wealthiest individuals, such as Mukesh Ambani and Ratan Tata. Patkar is running in northeast Mumbai, an area with a disproportionate number of the city's particularly abject slums and its largest garbage dumping ground.

Where do the two candidates meet? Have both women's positions evolved as they confronted the realities of party politics? Or were their views never as antagonistic to one another as it may have appeared? Or has the Aam Aadmi Party fundamentally changed the terms of engagement? The answer appears to be: a bit of all three.

"What unites Medha and me is the fundamental belief that the Indian people are very hard-working, innovative and entrepreneurial," Meera Sanyal told over the phone. "We don't need charity and handouts. What we do need is a level-playing field -- a society that has equality of opportunity."

Sanyal is among that minority of Indians with access to the best opportunities India offers. She went to elite south Mumbai schools, Sydenham College of Commerce and Economics and then took an MBA at INSEAD, a reputable business school in France.

The daughter of a decorated naval officer, Admiral GM Hiranandani, and a mother of two children, Sanyal had a three-decade career as a banker before resigning from her position as chairman of the Royal Bank of Scotland's India arm in December and as CEO in March last year in order to stand for elections.

She did not switch careers overnight. In 2009, she had stood from the same Mumbai constituency as an independent candidate, and lost. After that, while continuing to work at the bank, she began studying issues that she felt most required attention in the country and travelled extensively in order to understand people's concerns.

She speaks a language today that sounds closer to the one we are used to hearing from Medha Patkar, of social justice and equality of opportunity, while at the same time supporting a vibrant but corruption-free private sector. "Running through the AAP is this basic refrain – we want transparency, accountability, human dignity and equity," she said. "But we also want progress and growth. The common perception is that we are left-of-centre and anti-business. We are neither left nor right."

At the same time, not everyone agrees about all the issues, said Sanyal, who, given her background, has played a key role in drafting the party's economic policy, which its leader Arvind Kejriwal unveiled on Monday. "There are differences of opinion within the party," she said. "What is good is that there is a process of dialogue. Also, our economic policy is a work-in-progress that we will keep refining."

Ultimately, however, these abstract positions have to be tested against concrete issues, such as those that AAP has taken by the horns – foreign direct investment in retail, which it clearly stated it opposed even before the Delhi state elections, and the price of gas that the ruling United Progressive Alliance-II has agreed to pay Reliance Industries. The Aam Aadmi Party has filed a case against Reliance's chairman and managing director, Mukesh Ambani, and government ministers for allegedly revising the price upwards to give the company windfall gains at the public's expense.

What are Sanyal's views on these two matters? "The AAP party stand, as stated in our manifesto for Delhi is that we oppose FDI in retail," she said. But in practice, any impact of FDI in multi-brand retail at present, is theoretical, she added. Other than Tesco, the UK supermarket chain, which has planned a technical collaboration with the Tata group, there is no other large multi-brand retailer that has applied for permission to enter India.

Because there is the perception that there is so much corruption involved in setting up such activities in India, retailers like Tesco will find it impossible to actually do business here without flouting the UK's anti-bribery laws, she said. "In any case, my personal view is that we should first make India a better place for Indians to do business. Let us make it possible for Indian entrepreneurs to succeed in India, and automatically India will become a more attractive destination for foreign investment."

About the price of gas that Reliance will supply, she said that she hadn't studied the contract in detail. "But the evidence appears, on the face of it, damning to the company," she said. "Let's examine the facts. There was a policy on the basis of which tenders were invited and the fields were allotted. At the time, when the company won the bid, their share price shot up sharply. Presumably the basis on which the fields were contracted out was attractive enough that the equity markets thought this was lucrative in the company's favour. On what basis has the government now revised this contract?"

"You can't rewrite the rules mid-way through the contract to benefit the service provider at a cost to millions of consumers," she continued. "What has changed in the interim that forced you to revise the contract, and what is the impact on gas prices, which every consumer has to bear? Whether international prices go up or down should be immaterial if it was a cost-plus agreement based on a fixed capital investment."

Sanyal said housing, transport and open spaces were three problems that needed urgent attention in Mumbai. More than half the city's population lives in slums, while thousands commute in horrific conditions every day. She said she believed in public transport and that a lack of good governance was preventing the redevelopment of slums.

"Today, the slum lord controls the slum population," said Sanyal. "We have to dis-intermediate this and reach slum residents directly. In this city, a big portion of what is the middle class lives in slums. In any other country, they would be the backbone of the economy. I'm speaking as a hard-nosed banker, but if these people get a fair chance, your GDP will double. So we are strangling ourselves by not giving them the opportunities they want."