The frail 85-year-old retired school principal doesn't get out much. He walks slowly, reads books all day and watches patriotic soap operas by night. But India's liberal intellectuals call him a threat to democracy.

Dinanath Batra, dubbed "the book police" and "the Ban Man" by local media, is a self-appointed censor with wide influence. When he sends a legal notice to publishing houses informing them that their authors have injured Hindus' feelings, they listen. Fearing long court battles and violent protests by Hindu activists, they have withdrawn and pulped titles or asked authors to rewrite.

Batra has used India's loosely worded hate-speech and blasphemy laws to get allegedly offensive passages removed from textbooks and force Delhi University to drop from its syllabus an essay by an eminent scholar on an ancient Hindu epic. More recently, he got Penguin India to pulp a book on Hinduism by Wendy Doniger, a professor of religion at the University of Chicago.

Speaking in his secluded Delhi office at a school whose donors support his crusade, he says he wants to strip all books, including history textbooks, of anything he deems injurious to his Hindu faith. To him, it is a battle between good and evil.

"They call me the Ban Man. But my job is to create hurdles for evil as it sprints and spreads," said Batra, the founder of Shiksha Bachao Andolan Samiti (Save Education Struggle), a loose network of like-minded teachers, lawyers and Hindu nationalists. "We will not allow writers to insult Hinduism and our gods and goddesses under the excuse of scholarly research."

His mission has prompted concern among free-speech advocates about what they see as a growing climate of intolerance, as well as the possibility that Hindu vigilante groups will flourish under the Hindu nationalist government that came to power in May under Prime Minister Narendra Modi.

India's taste for censorship is not new: Salman Rushdie's novel The Satanic Verses was banned in 1988 because some Muslims called it blasphemous. But the country's taste has grown since then as different communities claim hurt and demand changes to song lyrics, movie titles, art exhibitions and books. The cross-currents now threaten to diminish India's increasing clout as a global intellectual centre.

Batra's most recent run-in has been with the publisher Orient BlackSwan over a decade-old history book that he claims includes inflammatory passages about the Rashtriya Swayamsevak Sangh (RSS), India's largest Hindu nationalist organisation, of which he is a member.

After they received his legal notice, the publisher startled authors by launching a fresh review of several books that it feared might draw a similar reaction, among them a book by Megha Kumar detailing sexual violence against Muslim women during religious rioting in the western state of Gujarat.

Mimi Choudhury of Orient BlackSwan said that the history book Batra objected to will not be withdrawn. But she added that Kumar's book might, in its current form, "attract prosecution" under the law Batra had cited that bars saying anything that might promote discord between communities.

Kumar said this raises larger questions about academic freedom in India.

"Nobody raised a legal objection to my book specifically, and yet the publisher cowed down and took a pre-emptive step," she said. "Will academic books be vetted by lawyers now instead of scholars? I am being asked to change the tone and language of sections of my book. My publisher's action can be construed as self-censorship."

A similar complaint by Batra against Doniger's book The Hindus: An Alternative History led to a court case that dragged on for four years. In February, Penguin India quietly settled with Batra out of court and pulped all copies of the book in India.

A protest near the US embassy in New Delhi against Wendy Doniger's The Hindus. Photograph: Anindito Mukherjee/EPA

India's constitution guarantees freedom of speech but with "reasonable restrictions" such as considerations of state security, decency and public order. But communities also routinely invoke laws that bar speech and written words that can be construed as insulting to a religion, inciting discord, according to Danish Sheikh, a researcher with the Alternative Law Forum.

In the past five years, Sheikh said, some groups have launched free-speech trackers to document assaults on freedom of expression. Others are now informally telling publishers not to panic when they receive a legal notice from someone such as Batra.

While Batra restricts himself to court battles, other protests have been violent. In 2004, Hindu activists vandalised a library in western India that had assisted the American author James Laine with his controversial book about a 17th-century Hindu king. In 2008, students roughed up a professor and broke windows in Delhi University's history department to protest against an essay on Hinduism that was later dropped.

Batra met India's new human resources minister, Smriti Irani, last month and asked her to overhaul school curriculums, offering to participate in consultations. Free-speech advocates find Batra's cosiness with the government worrying.

"What worries me is that Dinanath Batra is not a lone-runner. He has the ear of this government," said Arpita Das, publisher of Yoda Books, which specialises in books on LGBT narratives. "His opinion will be heard when school and university curriculum is prepared. This is a wake-up call."

Batra's strong Hindu nationalist ideology goes back to his early years. Born in Pakistan's North-West Frontier region (now known as Khyber Pakhtunkhwa), he was a teenager when bloody Hindu-Muslim rioting broke out after India and Pakistan were partitioned in 1947. The RSS, he said, tasked him and others with a mission to "protect the Hindus in Pakistan".

He "infiltrated incognito into Pakistani mosques to find out how the Muslims were plotting to attack Hindu refugees," he recalled. Based on the information he collected, he helped organise Hindus in Pakistan, taking them to safe areas, he said.

After he became a high school principal in 1955, he found textbooks that he said gave India's history a colonial slant – portraying local heroes in a negative light, for example. He campaigned to have the passages removed, and his career as a self-confessed education activist was born.

But Batra's battle may be overtaken by technology. Within hours of being banned, Doniger's book came out online.

"As soon as a book or essay is banned or withdrawn, everybody begins downloading and sharing it online," Das said. "Whatever Batra opposes suddenly finds an entirely new generation of readers."

This article appeared in Guardian Weekly, which incorporates material from the Washington Post