TORONTO - The secret law passed by Ontario's Liberal government surrounding police powers during the G20 summit in Toronto could have led to even more abuses than were witnessed, former chief justice Roy McMurtry concluded in a report released Thursday.

More than 1,100 people were arrested by some 20,000 police officers from across Canada who patrolled Toronto during the G20 weekend last June.

The public, and police, were both mistakenly left with the belief the law gave officers the authority to stop, search and detain anyone near the G20 security zone, and such searches took place across the city, well away from the fenced-in summit site.

McMurtry criticized the government for updating a Second World War law designed to protect public buildings like courthouses to give police additional powers, and then failing to tell the public.

"The Public Works Protection Act raises issues regarding the liberty and security of the person in providing for warrantless searches and stopping for identification," McMurtry writes in the report. "(The) potential for abuse is beyond troubling, to say the least."

McMurtry called the law "vague," and warned a vague law can lead to "inconsistent and arbitrary" enforcement.

"Individuals are not provided with sufficient guidance as to what behaviour a law prohibits," he said. "And those in charge of enforcing the law are not provided with clear guidance as to how to enforce it."

The Canadian Civil Liberties Association said McMurtry's report vindicates what it has been saying all along, that the secret G20 law "precipitated violations of civil rights throughout the city."

Protesters can't obey laws they don't know exist, said association general counsel Nathalie Des Rosiers.

"By using, cleverly, a piece of legislation which is obscure and outdated, I think it created significant misunderstanding and undermined the public's ability to obey the law," she said.

The civil rights group again called on Premier Dalton McGuinty to apologize for passing the secret law.

"There is a need to apologize to the Ontario public who were prevented from knowing that the law had been changed," said Des Roisers. "It would be a significant way of showing a recognition that something went wrong and that it ought not to have happened."

The government should also agree to call a full-scale inquiry into the G20, added Des Rosiers, who welcomed McMurtry's report but said it looked at only one aspect of police behaviour during the G20.

"It doesn't speak to the communications strategy of the police, the way in which the forces were deployed throughout the city, the decision to disperse peaceful protesters, to kettle them and the infiltrations of the different groups," she said. "The report points to the fact there were some significant failures during the G20 and we should get to the bottom of it so it's not repeated."

However, Community Safety Minister Jim Bradley said it would be up to the federal government to call a public inquiry into the G20, and he declined to apologize for passing the law.

"Our government has said over and over again that we communicated the law very poorly," said Bradley. "In my view, not promptly enough, not clearly enough, and the government regrets this very much."

Ontario's Progressive Conservatives called on McGuinty to apologize but rejected a public inquiry as too costly. The NDP, meanwhile, said it was too late for an apology but added that a public inquiry was the only way to clear up a "taint" left by the G20. The Tories also said former Public Safety Minister Rick Bartolucci should be fired from cabinet for his role in championing the secret law.

McMurtry found the federal government, the RCMP and provincial police all said extra powers for police were not needed, but Toronto police Chief Bill Blair wanted extra authority for the G20 weekend and the province granted it.

"I agree with the observation of the CCLA that the provisions of the (secret law) led to a lack of clarity as to the scope of the search and seizure powers which created many difficulties and conflicts that probably could have been avoided," writes McMurtry.

The government will scrap the "outdated" Public Works Protection Act after public consultations, and replace it with new legislation to protect courthouses and nuclear generating stations, said Bradley.

Ontario complained about locating the G20 in downtown Toronto almost immediately after Prime Minister Stephen Harper announced he was moving it to the city, and Bradley suspects even federal officials would now admit it was a mistake.

"When you have it in a downtown area of a large city such as Toronto, that certainly lays the groundwork for some extensive trouble," he said. "On reflection, even those who made that choice would today say it's likely would have been better to hold it someplace else."