Six high-risk prisoners escaped a Canadian jail last summer after spending four months chipping a path to freedom with nail clippers and other makeshift tools, according to a government report released.

The prisoners, four of whom faced murder charges, used their tools to remove a heating grill and steel plate and win access to a brick exterior wall.

While some inmates played cards at a carefully positioned table to block the guards' view, others chipped away at the wall, finally breaking through with a steel shower rod. They then used braided blankets and bed sheets to scale a wall of the compound and escape.

"Idle hands are the Devil's tools," said the Saskatchewan government report, referring to the fact that prisoners at the Regina Correctional Centre had little to do in the unit, which was built in 1964 and housed prisoners awaiting court dates.

"They tend to gravitate towards doing whatever they can get away with."

The report team made 23 recommendations, all of which the Saskatchewan government accepted. The government will spend C$87 million (£49 million) building a new centre in Saskatoon for prisoners awaiting court dates and C$9.4 million to bolster security equipment in prisons. The report said at least 87 prison workers had supervised the six prisoners' unit without detecting the escape preparations. Some guards had suspected something was being planned, but they did not interview the prisoners.

"It was shocking," said Saskatchewan Corrections Minister Darryl Hickie, a former police officer and prison worker.