OTTAWA - Canada's prison ombudsman says MPs need to ask harder questions about whether the country will get its money's worth from hugely expensive changes to the criminal justice system.

Federal politicians are agreeing to major changes that will cost billions of dollars on prisons over the next few years, says Howard Sapers, the Correctional Investigator of Canada.

"The question becomes, are you getting the best return on that investment?" Sapers said in an interview.

"What is it that we want out of our criminal justice system? We want safety in our communities. So, is building prisons the best return on investment? These are legitimate questions that have to be asked."

The impacts of the Conservatives' tough-on-crime agenda on federal and provincial budgets, prison populations and crime prevention are largely undocumented.

Public Safety Minister Vic Toews allowed this month that just one piece of the crime agenda -- C-25, the Truth in Sentencing Act -- will cost the federal government about $2 billion over five years.

The Parliamentary Budget Officer plans to release a report in coming weeks that will price that legislation at between $7 billion and $10 billion for provincial and federal governments over the next five years. The provinces are expected to shoulder most of the cost.

But that's just one act of more than a dozen that are changing the way the prison system works.

It's up to Parliament to get to the bottom of the issue, Sapers said.

"The real question in my mind right now is not just what is the cost of C-25, but what is the cumulative impact on federal corrections of all of the federal initiatives, and being thoughtful about costing those initiatives out," he explained.

"And I think that should frame the debate about whether or not (it) is a good return on investment."

Kim Pate, who heads the Canadian Association of Elizabeth Fry Societies, goes even further. She says Parliament is responsible for "egregious breaches of fiduciary responsibility" for passing laws without researching what the true costs are.

Toews has said repeatedly that even as the federal prison population rises, costs will be kept down by double-bunking inmates and expanding existing facilities.

Extra prisons will be built as necessary, he says. And the price tag is worth it because the crime legislation will keep dangerous people off the streets.

But double-bunking is not an acceptable answer for Sapers, Pate and others concerned about the state of the country's prisons.

About 1,300 federal inmates are already double-bunking in cells built for single occupancy, Sapers said. That's about 10 per cent of the total population and the doubling-up is concentrated mainly in medium-security facilities, primarily in Ontario.

Canada has signed a United Nations agreement that specifically prohibits two inmates to a cell and Canadian policy generally conforms with that agreement.

Experts have argued that cramming two or more prisoners into a cell creates dangerous conditions, not just for the inmates, but also staff, and for the general public that will have to accept more volatile prisoners after their release.

"From our experience, when double bunking goes up, the climate in the institution becomes more troubling," Sapers said. "So there are more complaints, there are more grievances, there is more violence, there are more security incidents."

Toews has said he does not have a problem with double-bunking. He has also said he has a rough idea of what the total cost of the tough-on-crime agenda will be, but will not say what the cost is.

When senators have asked for estimates in the past, they have been told that the information was confidential because it was before cabinet.

The federal budget set aside about $90 million over two years to expand prison capacity.