The high court said Friday it won't hear reporter Jim Bronskill's appeal in his long-running fight to have more information in the Douglas file made public.
Paul Champ, the news agency's lawyer, said the refusal to hear the appeal was disappointing.
"This decision is a blow to the study and understanding of Canadian history," he said.
Bronskill has been fighting since 2005 for access to the decades-old, 1,149-page file compiled on Douglas by the now-defunct RCMP Security Service from the 1930s until just before his death in 1986.
Parts of the dossier that have been released show the Mounties shadowed Douglas for years. They attended his speeches, analysed his writings and eavesdropped on private conversations.
They were particularly interested in his links to the peace movement and the Communist party.
Library and Archives Canada, which now holds the file, initially released only 400 heavily censored pages on Douglas, a former Saskatchewan premier, first federal NDP leader and father of medicare.
An additional 300 pages were released in 2011, just before the case was heard by the Federal Court. Even more were disclosed after the court ordered that more should be made public but large portions of the file remain secret.
The Canadian Security Intelligence Service, which replaced the RCMP security arm and advised Library and Archives on release of the Douglas file, argued vehemently against full disclosure.
Although some information in the file goes back a lifetime, CSIS argued that uncensored release would reveal secrets of the spy trade, jeopardize the lives of confidential informants and compromise the agency's ability to conduct secret surveillance.
"I still don't know how documents over 70 years old can present a risk to national security today," Champ said.
Federal Court Justice Simon Noel ruled that Library and Archives, in deciding what to release, failed to take into account its mandate to make historically significant documents accessible. He reviewed the whole file and attached an annex to his ruling listing the pages that contained information he believed should be further disclosed.
However, Noel's ruling was curtailed last October by the Federal Court of Appeal, which also struck down his annex.
The government argued there was no need for the Supreme Court to hear the matter because there was "no issue of public importance" in the case.
Champ said he thinks otherwise:
"As a result of this judgment, hundreds of documents about an important historical figure will remain permanently hidden away from the Canadian public, or at least for all of our lifetimes."
He noted the Douglas family backed the effort to bring the file into the open.
"This case had the full support of the Douglas family and Canadian historians from across the country," he said. "It opened the doors of Library and Archives a crack, but we were hoping to swing them wide to the study of history.
"Maybe a future case will establish that any censorship of history is wrong. A democratic country should be able to look truthfully at its past and learn from it."
As is usual in leaves to appeal, the Supreme Court gave no reasons for refusing to hear the case.
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