OTTAWA - Bruce Carson was cleared to work for Stephen Harper by a mid-level bureaucrat without the involvement of senior security people or anyone in the Prime Minister's Office, says a spokesperson from the Privy Council.

The Privy Council Office also says it's conducting a review of its security-screening procedures in the wake of controversy over Carson's criminal record.

Harper called for just such a review earlier this week after The Canadian Press revealed that Carson had been convicted on five counts of fraud -- three more than generally known -- and received court-ordered psychiatric treatment before becoming one of the prime minister's closest advisers.

Harper said he'd known of two fraud convictions in the early 1980s, for which Carson was jailed and disbarred. But he said he wouldn't have hired Carson had he known the 65-year-old had also been convicted on three more counts of fraud in 1990.

Carson, who left the PMO in 2008, is currently embroiled in allegations of illegal lobbying. Harper referred that matter last month to the RCMP.

Just who gave Carson his Secret-level security clearance had been a mystery that preoccupied much of Ottawa. Carson told The Canadian Press earlier this week he disclosed his entire criminal record when he applied for security clearance in 2006 and also discussed the matter with Ian Brodie, then Harper's chief of staff.

Harper and Brodie have both said they knew nothing about the 1990 convictions and weren't involved in granting clearance, which is generally handled by the dozens of staffers in the PCO security office.

Some reports suggested William Elliott -- then national security adviser at PCO and now head of the RCMP -- gave the green light to Carson. However, a senior intelligence official with direct knowledge of the matter told The Canadian Press that was not the case.

In the clearest explanation to date, PCO spokesman Raymond Rivet said "no senior officials in PCO, including the national security adviser at the time, and no PMO officials, were involved in granting the security clearance to Mr. Carson."

He later clarified that a director of security granted the clearance.

Rivet added in an email that PCO is "now conducting a review of the security screening procedures (specifically)."

Rivet's explanation is consistent with what one insider close to the situation has told The Canadian Press. The insider has said Secret-level clearance is almost never denied, even for someone with a criminal record -- provided the individual admits past transgressions.

Moreover, he's said Carson's past would not have stood out as something worthy of a red flag and likely wouldn't have been brought to the attention of anyone high up in either the PCO or PMO.

Out on the campaign, opposition leaders have been having a field day with the Carson affair, maintaining it shows Harper's judgment can't be trusted.

On Thursday, both the Liberals and New Democrats pounced on a Toronto Star report that Carson had been Harper's point man on Canada's combat mission in Afghanistan, participating in daily telephone briefings with senior defence, foreign affairs, RCMP, justice and corrections officials. They questioned how Carson could have been privy to top secret information on the mission with only Secret-level clearance.

"Harper defied the will of Parliament and refused to hand over documents related to Afghanistan to the elected representatives of the Canadian people," noted Liberal foreign affairs critic Bob Rae.

"But he apparently saw no problem in handing over the most sensitive of files to a five-time convict with absolutely no experience in foreign affairs, defence matters, diplomacy or development."

However, another source close to the situation noted that Carson was responsible for preparing for question period each day and the daily calls involved "information that would later become public" and "often ended up in question period."

The source said Top Secret information would not have been discussed on "an unsecured telephone line," even if Carson and the others did have sufficient clearance.

Most of the information that passes through PMO is classified as Secret; "Top Secret information is extremely rare, actually," the source said.

Intelligence material that could reveal confidential methods of gathering information would be Top Secret but the insider said such material was usually "cleansed" of compromising details so that it could be more widely distributed. In that way, even a briefing on a planned military operation in Afghanistan could be classified as Secret.

Carson worked for Harper when the Conservatives were in Opposition, helped on the transition team that smoothed Harper's takeover of power in 2006 and went to work in the PMO for the following two years as Harper's senior policy adviser and troubleshooter.

He left the PMO in 2008 to head the federally funded Canada School of Energy and the Environment in Calgary.

Last month, Harper asked the RCMP to investigate Carson after the Aboriginal Peoples Television Network alleged the 65-year-old may have illegally lobbied the federal government on behalf of a company that employed his girlfriend, a 22-year-old, one-time escort.