The country’s highest court has once again stirringly defended common law’s Great Writ — habeas corpus — and stuck another thumb in the federal government’s eye.

In a unanimous decision Thursday, the Supreme Court of Canada said prisoners should be given broad leeway to challenge decisions by their jailers, ignoring concerns about them flooding courtrooms.

Writing for the eight-member bench, Justice Louis LeBel said there might be concurrent jurisdiction between the Federal Court and provincial superior courts on some issues, but what’s important is access to justice for prisoners.

“Habeas corpus has become an essential remedy in Canadian law,” LeBel emphasized, protecting fundamental rights that belong to everyone “including those serving prison sentences.

“Habeas corpus is in fact the strongest tool a prisoner has to ensure that the deprivation of his or her liberty is not unlawful. This remedy is crucial to those whose residual liberty has been taken from them by the state, and this alone suffices to ensure that is rarely subject to restrictions.”

The decision was hailed by prison rights advocates who intervened in the case to oppose Ottawa’s appeal aimed at limiting the use of habeas corpus.

It was another stinging defeat for the Conservative government at the hands of a court that has recently turned thumbs down on its appointment of Marc Nadon and its law, the Aboliton of Early Parole Act.

“This has been hotly contested by the department of justice for 30 years,” explained Michael Jackson, a lawyer for the B.C. Civil Liberties Association.

“It’s the third time it’s been before the Supreme Court and one of the things I said to the court last fall is, ‘I’m getting tired of coming back to re-argue this point in the face of the federal government’s resistance to the idea of an effective speedy remedy for our prisoners.’”

In this case, a first-degree murderer filed a habeas corpus writ in 2010 after he was transferred from medium security Mission Institution back to maximum security Kent.

The warden said the move was required because she believed Gurkirpal Khela, convicted in the 2002 murder of Delta teacher Gary Sidhu, had paid two fellow prisoners three grams of heroin to stab another inmate several times.

But the B.C. Supreme Court in May 2010 ordered Khela returned to medium security because the warden didn’t disclose enough evidence to Khela about the accusations to justify her decision, a ruling largely upheld by the B.C. Court of Appeal.

The government appealed saying a superior court was the wrong forum — that Khela should have gone to the Federal Court with his complaint — and the courts got it wrong about the warden’s disclosure duty.

LeBel dismissed both arguments, underscoring the risk of circumscribing habeas corpus — Latin for “you may have the body” — the centuries-old legal sword of the wrongly imprisoned.

At issue here was not so much the warrant or its reach but whether federal prisoners should have access to the provincial superior courts.

“To get to Federal Court you have to exhaust the internal procedures that take months and months,” Jackson explained. “Hopefully this is the last time the Supreme Court is going to have to clearly say prisoners can choose the most effective and speedy access to get justice.”