A federal official has dropped a political bombshell on Parliament, alleging suspects handed over by Canada to Afghan authorities were tortured - and that the government was at best indifferent and at worst tried to cover it up.

Richard Colvin, an intelligence officer based in Washington who spent 18 months in Afghanistan in the No. 2 diplomatic post, delivered the stunning revelations to a packed committee room Wednesday.

His calm, precise recitation to the special House of Commons committee on Afghanistan directly contradicts nearly three years of assurances by the Conservative government that there was no credible evidence prisoners handed over to local authorities were abused, in violation of international law.

Colvin said the sweeping roundups of prisoners - many of them likely innocent - and their subsequent abuse has driven a wedge between Canada and the people of Kandahar, and destroyed much of the good will soldiers have fought and died to achieve.

"In my judgment, some of our actions in Kandahar, including complicity in torture, turned local people against us," he told a hushed room, where opposition MPs sat with mouths wide-open at what they were hearing.

"Instead of winning hearts and minds, we caused Kandaharis to fear the foreigners."

And he warned ominously that "Canada's detainee practises alienated us from the population and strengthened the insurgency."

In a meticulous seven-page opening statement, Colvin picked apart the handling of the prisoner issue by the Conservative government and the military, starting with the assurance that no torture had taken place.

He told MPs that captives taken by Canadian troops and handed over to the Afghans were subjected to beatings and electric shocks in 2006 and early 2007.

"According to our information, the likelihood is that all the Afghans we handed over were tortured," he said. "For interrogators in Kandahar, it was standard operating procedure."

Colvin said he remains concerned because Canada continues to hand over its prisoners to the National Directorate of Security, Afghanistan's notorious intelligence service.

In subsequent visits to a prison in Kabul, he said he personally spoke with several prisoners who claimed to have been abused. Out of the four inmates who were presented to him by Afghan authorities, he was certain that only one had been captured by Canadians.

Colvin was careful not to blame Canadian soldiers for carrying out the transfer orders, rather accusing the civilian and military leadership of creating the legal framework and policies that created the danger.

In a blistering indictment, he said the Red Cross tried for three months in 2006 to warn the Canadian army in Kandahar about what was happening to prisoners, but no one would "even take their phone calls."

"When the government is presented with credible evidence, we act on it," Prime Minister Stephen Harper's spokesman Dimitris Soudas, said in Zagreb, Croatia, for a refuelling stop en route back to Canada from New Delhi.

"And that's what we did three years ago when we signed the detainee agreement."

Canada took a staggering amount of prisoners, roughly six times more than British forces and 20 times more than the Dutch, he told the committee.

The vast majority of them were not "high-value targets" such as Taliban commanders, Al-Qaida operatives or bomb-makers, but rather ordinary Afghans, many with no connection to the insurgency.

Some of them may have occasionally carried a gun for the Taliban, either having been bought or coerced, he said, but many were farmers, truck drivers and peasants "in the wrong place at the wrong time.

"In other words, we detained and handed over for severe torture, a lot of innocent people."

Colvin painted a dramatic picture of institutional indifference that morphed into an exercise in damage control by the federal government once allegations of abuse became public in April 2007.

He said he was ordered not to write about prisoners, and soon afterward reports from the field began to be "censored" and revised to the point where diplomats could "no longer write that the security situation in Afghanistan was deteriorating."

Conservative MPs on the committee were indignant and said Colvin's testimony amounted to hearsay. They insisted he had provide no "first-hand" proof of torture, despite having seen bruises and other marks of abuse on the prisoners he interviewed.

"It's all second hand," said Tory MP Laurie Hawn, a former military officer. "I really have to question whether this is credible."

Fellow Conservative MP Cheryl Gallant dismissed all of the testimony as something that wouldn't be admissible in court and tried to paint Colvin as a Taliban dupe.

"They know how to take and plant false stories, how to push stories out," she said reading from previous testimony given by a military officer to the Commons defence committee.

"It's called information operations."

Hawn, who is the parliamentary secretary to the defence minister, questioned why Colvin never raised his concerns directly with cabinet ministers when they visited Afghanistan.

"It would be a bit inappropriate, I think, to ruin a minister's visit by coming and saying, 'Hey did you know people are getting tortured with electricity?"' Colvin answered.

But Hawn said it's exactly the kind of information ministers would want to know.

Liberal defence critic Ujjal Dosanjh described the Conservative response as "despicable" and an attempt to shirk their responsibility.

"There is something called ministerial accountability. You can't be ignorant. You can't be dumb. You can't shut your ears, your ears and your mouth to say 'No, I didn't know."' Dosanjh said.

Before Colvin's testimony, opposition MPs attacked the Conservative government during question period, accusing it of orchestrating a cover up.

Senior ministers tried to deflect the blame to the former Liberal government, which instituted the original transfer agreement that provided Canada with no means of checking on its prisoners.

"We inherited an inadequate transfer arrangement left in place by the previous government," said Defence Minister Peter MacKay.

But the opposition zeroed in on the orders to hold back information, as outlined in a story by The Canadian Press on Tuesday.

They demanded to know the names of the officials who tried to shut down Colvin's reports and sanitize the reports of other diplomats. Colvin had filed reports in 2006 warning of the torture, but MacKay, Prime Minister Stephen Harper and other cabinet minister say they were never informed and first heard such allegations in 2007.

"Who in this government issued that order?" asked Dosanjh. "Why is this government creating a culture - an un-Canadian culture - of secrecy about an issue as abhorrent as torture?"

Peter Kent, parliamentary secretary for foreign affairs, called it an "outrageous" question and denied there was a coverup. He said since the new transfer agreement was signed, the government has received no complaints of torture.

But Ottawa did halt the transfer of prisoners in the fall of 2007 when a prisoner was found to have been tortured. It is the only case of abuse the Conservative government has ever been willing to acknowledge as "credible."

Yet, prison visit reports - leaked to The Canadian Press on Wednesday - suggest that other cases came to light between April and October of 2007 as Canadian officials stepped up inspections of Sarpoza prison and the separate Afghan intelligence jails.

Several prisoners complained of being abused during that timeframe and one even showed officials bruises on his back, but the allegation were chalked up as being unverified.