Under a scorching summer sun, a swarm of 400 furious women engulfed the scruffy electricity office of Banda district in north India. They were all dressed identically in fluorescent pink saris. For more than a fortnight they and their families had had no electricity, plunged into darkness at dusk and stewed in sweat at dawn. But they had all been sent bills demanding payment for power they had never received.

It was at noon one day last May that the group, brandishing sticks, first surrounded and then charged into the office, punching the air and shouting slogans of solidarity. They wanted to confront the officer in charge but met instead his cowering juniors, at whom they bawled to telephone the boss. When the man refused to come to the office, the women became incensed. They snatched the office key, roughed up the terrified staff and, after herding them outside, locked the door and ran away, vowing to return the key only when they had electricity again.

There are few places on earth where life is as short and brutal as in Bundelkhand, the desolate region straddling the southern tip of Uttar Pradesh where Banda lies. Farming is the principal livelihood; wages are as little as 60p a day for men and half that for women. Bonded and child labour are rife. Corruption is routine. Its reputation in India is that of a place where people still die of hunger.

But what has made Bundelkhand infamous is banditry. Scores born out of feudalism and caste violence are settled by bullets. It was here that Phoolan Devi, the Bandit Queen of India, used to lead her gang of robbers in vicious acts of retribution on rich, upper-caste villagers. Products of this cruel environment, the hundreds of pink-clad women knew that their electricity supply had been disconnected by corrupt officials to extract bribes from them to get the power switched back on. With no functioning law to fall back on, they knew also that the only way to get a power supply was to take matters into their own hands. Within an hour of their absconding with the key, the electricity was restored.

It is just one victory in a list of successes achieved by the Gulabi Gang since it formed two years ago. Gulabi means pink, and refers to the electric shade of the uniform worn by the 500-plus members, who hail from Banda's arid villages. The women have become folk heroes, winning public support for a series of Robin Hood-style operations. Their most daring exploit was to hijack trucks laden with food meant for the poor that was being taken to be sold for profit at the market by corrupt officials.

The targets of the Gulabi Gang's vigilantism are corrupt officials and violent husbands. The gang has stopped child marriages, forced police officers to register cases of domestic violence - by slapping them - and got roads built by dragging the official responsible from his desk on to the dust track in question.

The gang is led, and was created by, 46-year-old Sampat Devi Pal. When I meet her, she is demonstrating self-defence moves with a stick. "We always carry them but only for protection," she explains, twisting the weapon high over her head and thwacking it hard against her opponent's.

The daughter of a shepherd, Pal was put to work on the family's land while her brothers went to school. Married at 12 to a 20-year-old man from a neighbouring village whom she had never met, she was pregnant by 15. She wanted to be sterilised after having two daughters but her mother-in-law wouldn't allow it until she had produced a son. Another four children followed.

As is common among Hindu families in rural north India, her in-laws wanted Pal to veil her face and remain silent in the presence of male family members, as a sign of respect for authority. "I never did either," she giggles throatily.

Pal is difficult company. Those not showing her the utmost respect get crude abuse. Yet in a place where expectation of female restraint is so faithfully observed, only someone as irascible as Pal could defy it. I meet her husband in the couple's home, which is built in a ditch with plastic sheeting for a roof. He is mute and utterly obedient to her every order. Later, an astonishing role reversal takes place as half a dozen loyal and obedient male hangers-on are sent running at the snap of her fingers to fetch us tea and guavas.

To them Pal is someone who can defend the weak, which, in the badlands of Bundelkhand, is rare indeed. Although 80% of the gang's actions are on behalf of women, they are increasingly called upon by men. When 7,000 Banda farmers decided to take to the streets to demand compensation for failed crops earlier this month, they asked the Gulabi Gang to be there.

The gang's challenge to the throttling grip of male authority has brought new confidence - and dangers - to its members. I meet Radha, 40, the leader of the ambush on the electricity office, walking with a friend in the market. "Before I joined the gang I was in purdah and never went out of the house," she says. "Now I've tackled ministers and officials and I've done away with my shyness - and the veil." Others have been less fortunate. A few days before I arrive in Banda, one of the gang's youngest members, a 14-year-old girl, had been attacked with a sickle as she went for her morning ablutions in the fields. She had put up a fight when a 16-year-old neighbour tried to rape her.

Meanwhile, Pal herself is in danger of being criminalised. Following a complaint by the police, she is waiting to hear if she will be formally charged with 11 offences, including unlawful assembly, rioting, attacking a government employee and obstructing an officer in the discharge of duty."To face down men in this part of the world, you have to use force," Pal says. "I didn't do anything wrong. I have faith that justice will prevail."

It took Pal over a decade to muster the foot soldiers for the gang she now calls her "army". Travelling from village to village, she amassed hundreds of female fans by belting out her repertoire of protest songs. "I wanted to lift them out of the black hole they'd been pushed into," Pal says, like a true orator. Only 20% of women in Bundelkhand's villages can write their name and most are child brides. "I realised that without education, women are steeped in superstitious beliefs."

Eventually, hundreds of women were turning out to hear Pal. They also brought their problems: land grabbing by powerful thugs that left whole families homeless; their violent husbands' alcoholism and drug abuse; how officials demanded bribes even for payment of a widow's pension.

"I realised that if I could have this kind of control over women then I could get them out of the clutches of their husbands," Pal says, narrowing her eyes. There is not the faintest hint of a smile on her lips.