LONDON — A decision by the British Library not to host a huge collection of Taliban-related documents, despite years of close involvement with the project, has added to concerns that Britain’s sweeping body of antiterrorism legislation is impinging on academic freedom.

Over nearly a decade, a group of researchers who organized the Taliban Sources Project have painstakingly collected and translated into English more than a thousand newspapers, magazines, radio broadcasts, military and administrative documents, as well as handwritten poetry by Taliban fighters in Afghanistan. The group’s aim is to digitize the primary material, shedding light on the Taliban’s organization and the insurgency in Afghanistan.

The British Library has one of the world’s biggest digital collections, including manuscripts that date back centuries. The researchers took the project to the library in 2012, received advice from a prominent scholar and appointed members of the library to its advisory board. But a month ago, the library declined to take on the project, saying it had been legally advised not to publish the collection because it contains material that could be in breach of Britain’s antiterrorism laws.

The library said that it recognized the archive’s research value. But “it was judged that it contained some material which could contravene the Terrorism Act,” it said in a statement, “which would present restrictions on the library’s ability to provide access to the archive for researchers.”

The Terrorism Act “places specific responsibilities on anyone in Britain who might provide access to terrorist publications,” the statement added, “and the legal advice received jointly by the British Library and other similar institutions advises against making this type of material accessible.”

The Taliban Sources Project mostly focuses on material from 1994 to 2001 that “gives a unique window into the Taliban’s world views, their negotiations with foreign governments, how they viewed history,” said Felix Kuehn, an organizer of the project, adding that the material could help provide a more complete picture about the organization in the run-up to the 2001 American invasion of Afghanistan.

“Our knowledge of the Taliban in the 1990s is dominated by Western media coverage that was highly politicized, in part because information was not easily accessible,” Mr. Kuehn said.

The project’s 10-member team has translated more than two million words of material. The group had hoped that the British Library would “provide a big institutional home for the material for the long run,” Mr. Kuehn said, calling the decision disappointing. “We can put it up on the web, too, but it wouldn’t last forever.”

Another organizer of the project, Alex Strick van Linschoten, who has written extensively about the insurgents, pushed back against any implication that the project would be of use to potential terrorists, saying that the collection contains “no recipes for making bombs or anything like that.”

David Anderson, the independent reviewer for Britain’s antiterrorism laws, said Friday that the Terrorism Act was a broad law that could be even more broadly interpreted “by police and lawyers who want to give cautious advice.” Such interpretations could easily impinge on academic freedom, he warned.

“If this law were interpreted to prevent researchers from accessing Taliban-related material that would impact their academic work, it would be very regrettable,” he said. “That’s not how academics work.”

The Terrorism Acts of 2000 and 2006 make it an offense “to collect material which could be used by a person committing or preparing for an act of terrorism” and criminalize the circulation of terrorist propaganda. But under the laws, the police must show evidence that the owners intend to use the publication for terrorist purposes, and that they have a reasonable excuse to possess it, Mr. Anderson said.

He raised the example of Rizwaan Sabir, a graduate student in Nottingham who was detained in 2008 under the Terrorism Act after being accused of downloading terrorist material. Mr. Sabir had downloaded an Al Qaeda training manual as part of the thesis he was writing about terrorist strategies. The police later apologized and paid him compensation for false imprisonment.

This year, a group of lawmakers criticized government proposals to ban extremist speakers from university campuses, saying they, too, would seriously restrict academic freedom of speech.