Federal inmates have been granted wide scope to go to court to challenge decisions affecting their detention, such as transfers to higher-security prisons or placements in segregation.

In a major victory for prisoners' rights, the Supreme Court of Canada stressed that the nearly 1,000-year-old tradition of habeas corpus – the right to go before a judge to argue against illegal detention – means that prisoners deserve a prompt and thorough court hearing.

"No one should be deprived of their liberty without lawful authority," Justice Louis LeBel said in an 8-0 ruling on Thursday.

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The ruling is the latest in a series of decisive defeats for the federal government at the hands of the country's top court, and is especially important as the number of federal prisoners rises steadily, and prison violence and use of restrictions such as segregation rise along with it. "It's an important counterbalance to a political agenda of undermining prisoners' rights," Michael Jackson, who teaches law at the University of British Columbia and represented the British Columbia Civil Liberties Association, which made arguments in the case, said in an interview.

Gurkirpal Singh Khela was convicted of first-degree murder for hiring two men to carry out the 2002 killing of school teacher Gary Sidhu. In 2009, after the B.C. man was transferred to Mission Institution, a medium-security prison, from the maximum-security Kent Institution, prison authorities received information from three anonymous sources that he had hired two men to stab another prisoner in retaliation for an assault when he was at Kent, and paid them with three grams of heroin. He was transferred in February, 2010, and challenged the transfer in court, saying the warden had not disclosed enough information about the allegations to allow him to fight them effectively.

Public Safety Minister Steven Blaney and Justice Minister Peter MacKay did not respond to requests for comment on Thursday. The federal government had argued that prisoner complaints should be put to a grievance process within corrections, followed by a request for review to Federal Court, which could take months or years to be heard, if at all. The Supreme Court said prisoners could take their challenges to provincial superior courts, which happen within six days, according to lawyer Bibhas Vaze, who represented Mr. Khela.

Ottawa had warned that giving prisoners expanded access to provincial superior courts would add needlessly to cost and complexity, and compromise efficient justice. It also said prison authorities could not give out much information because they rely on confidential informers.

The court stressed that judges should not try to micromanage prisons. But it said prison authorities bear the burden of showing that their transfer decisions, and other restrictions on prisoners, are carried out with fair process, including giving the prisoners summaries of the evidence on which they relied. It also said the judges have the power to decide whether the prison authorities' decisions were reasonable.

The B.C. Civil Liberties Association called the case an "important chapter in the long and continuing struggle to ensure that the rule of law runs inside Canadian prisons." It cited inquiries into the 2008 death of teenager Ashley Smith in Ontario, an inquiry in the strip searches of female prisoners in the 1980s and other inquiries as far back as the 1840s, and said timely oversight by judges can help prevent abuses.