The Supreme Court of Canada has unanimously decided that the federal government cannot be dragged into court cases against tobacco companies and be held partly liable for any damages.

Imperial Tobacco Ltd. and other tobacco companies had raised 10 arguments in their court filings about why the federal government should be named as a "third-party" co-defendant in lawsuits against the companies. But the court struck down every argument.

"On all counts, the Supreme Court of Canada ruleds that no, Ottawa is not responsible when these cases go to trial," reported CTV's Roger Smith from outside the courthouse in Ottawa Friday morning.

"This is a big victory for Ottawa and a big loss for the tobacco companies."

The Supreme Court's ruling referred to two cases in which tobacco companies wanted to name the feds as "a third-party defendant," so that the government could be held partially liable for any damages that might be found against the companies.

One case involved a class-action suit brought against Imperial Tobacco almost 10 years ago by smokers who say they were tricked into thinking "mild" or "light" cigarettes were less harmful than regular cigarettes. The smokers want a refund for the costs of those cigarettes, as well as punitive damages.

The other case concerns a lawsuit brought by the British Columbia government itself against tobacco companies, which seeks to recoup billions of health-care dollars spent on treating smoking-related diseases.

That suit is expected to act as the lead case in similar lawsuits against the tobacco companies brought by three other provinces: Ontario, New Brunswick, Newfoundland and Labrador. Nova Scotia, Manitoba, Quebec and Alberta have also announced their intention to pursue lawsuits.

In both cases, the tobacco companies argued that the government of Canada had been "a senior partner" of the tobacco industry for decades, by legalizing tobacco, regulating it, and taxing it. They argued that it only made sense that the government be accountable as well.

Imperial Tobacco argued in the first case involving "light" cigarettes that Health Canada had directed it to make and sell "light" brands.  Health Canada agreed to warning labels on cigarettes in 1967. It also advised smokers to switch to light or mild brands because they were less harmful.

The federal government also helped to develop the strains of tobacco used in "light" cigarettes. It then collected licensing fees and royalties from the sales, as well as the tax revenue.

Rob Cunningham, a senior policy analyst with the Canadian Cancer Society, says his group is "very pleased" with the judgment.

"It's a very significant defeat for the industry, and we're a step closer to actually getting these medicare cost recovery cases to trial, and that's very important," he told CTV News Channel.

Cunningham said he didn't agree with many of the tobaco companies' arguments about why the federal government should bear partial responsibility for smoking-related costs.

"It is the industry that has deceived governments over many years, hiding their internal research about cancer, about nicotine, about so-called light and mild cigarettes," he said.

"If the industry had come clean in the ‘50s and ‘60s, smoking rates would have come down much faster and there would be less disease and less health care costs."

Imperial Tobacco Canada Ltd. has not yet offered a response to the ruling.