As four former prime ministers called for renewed efforts to enhance the oversight of national-security agencies, Prime Minister Stephen Harper said on Thursday that he prefers the status quo.

Mr. Harper faced repeated media questions about oversight – including references to the letter published exclusively in The Globe and Mail.

"In Canada, I believe we've had a superior model of oversight based on independent, expert third-party advice," Mr. Harper said, after an unrelated announcement at Kwantlen Polytechnic University in Surrey, B.C.

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The Globe letter was written by Jean Chrétien, Joe Clark, Paul Martin and John Turner and published Thursday.

Mr. Harper did not specifically refer to the text of the letter in which the former leaders say that protecting public safety is a key role of government, but "the lack of a robust and integrated accountability regime" for Canada's national security agencies makes it difficult to assess their efficacy and legality.

They say that efforts to enhance parliamentary oversight of national-security agencies have been unsuccessful but Canada needs independent oversight and effective review mechanisms more than ever.

Asked about oversight in Bill C-51, anti-terror legislation to expand the powers of security agencies, Mr. Harper noted that many additional powers in the legislation require judicial authorization – a line of argument that the Conservatives have repeated in defending their approach.

"We're strengthening oversight already but the model we have in Canada of independent expert oversight, that's the model we're pursuing. We're going farther in that direction and we, as a government, are not interested in politicians doing the oversight."

He added: "We're not going to move to a model where politicians do the oversight."

Four of five Canadians surveyed for a new Angus-Reid polls said they support C51, but two thirds also said they believe there should be more oversight. The same number told the pollster they trust security agencies to properly use powers.

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The NDP has said it will vote against the bill while the Liberal Party says it will support the bill, despite the lack of parliamentary oversight of the Canadian Security Intelligence Service.