Money talks, especially in the bustle of an Indian bazaar. But what would you do if someone thrust a note in your hand that on close inspection turned out to be worth nothing at all? Astonishingly, but for good reason, there are now millions of zero-rupee notes in circulation in India.

But what on earth is the point of a zero-rupee note? What are they used for? Who printed them and what do they mean? In fact, these apparently frivolous notes turn out to be a key weapon in the fight against corruption.

Anti-corruption is a major enterprise in India today. In 2009 the social reformer Anna Hazare spearheaded a huge anti-corruption movement across the country. Hazare called on the Indian government to introduce a lokpal – a type of public ombudsman committee – with the legal power to investigate government corruption.

There have also been numerous village-level and regional movements, using public interest legislation and the 2005 Right to Information Act to counter corruption where it occurs.

But campaigners are also getting creative. In 2007 an NGO called 5th Pillar came up with the idea of printing bank notes with a value of zero. They look a lot like the 50-rupee notes: They carry a picture of Gandhi and are a similar colour. But they are, literally, not worth the paper that they’re printed on.

When an official demands a bribe, a citizen can present the zero-rupee note as payment. The note carries the warning: “I promise neither to accept nor give a bribe.” In theory, officials will be compelled to reflect on their actions when presented with the note, and they will be shamed into recognising the illegality of their demand.

The NGO’s website carries numerous examples of where this tactic has been effective: even hardened bribe-takers are sometimes persuaded to change their practices. By August 2014 there were reputed to be 2.5m zero-rupee notes in circulation. So successful has the note been that it is now being adopted in places as diverse as Nepal, Ghana, Benin, Mexico and Yemen.

But will this initiative bring about real change? During the past 20 years I have been carrying out research in the state of Uttar Pradesh, where corruption is intense, varied and entrenched. Most of my friends say that the zero-rupee note movement will have little effect, “Corruption is corruption,” they say, “no one will be put off by getting a zero-rupee note.”

People are more pragmatic than in the 90s. 'It is alright to be corrupt,' they say. 'As long as you avoid fraud'

In the past two decades senior officials have appropriated vast sums in Uttar Pradesh, and more broadly in India, in everything from second-generation mobile phones and cricket’s Indian Premier League to rural healthcare. According to some estimates, the opportunity costs of corruption in terms of lost investment growth and jobs are $50bn in India every year.

At the ground level, bribery is a daily ritual for many Indians. Government bureaucrats demand payment for providing services that should be free. They embezzle money earmarked for development projects. And police officers routinely demand “tips” – known euphemistically as “money for water and tea”.

A portion of the money collected on the ground is passed up through state hierarchies and on to politicians, who use the funds to finance elections. In this system, it is very difficult to avoid becoming corrupt.

Many anti-corruption organisations themselves become corrupt. Just a few days ago the AAP – the Aam Aadmi, or “Common Man”, party – a motley assortment of activists and intellectuals vigorously opposed to corruption – became mired in rumours of favoritism and power-grabbing.

Corruption may actually be getting worse. Economic growth in Uttar Pradesh has led to spiralling corruption. Rising inequality has increased frustration, especially among low-ranking government officials and the unemployed. People are more pragmatic now than they were in the 1990s. “It is alright to be corrupt,” they sometimes say. “As long as you avoid fraud.” “Corruption” refers to the ordinary system of kickbacks and bribes; “fraud” is where an official takes a bribe and still does not act.

Zero-rupee notes may be having an effect, however marginal. But Salman Rushdie’s aphorism remains as true as ever: “Indian democracy: one man, one bribe”.