If Prime Minister Stephen Harper did not know about the cheque written by his former chief of staff to cover the improperly claimed expenses of Senator Mike Duffy, federal accountability guidelines written by his government suggest he does not need to shoulder responsibility.

When the Conservatives first took power in 2006, Accountable Government: A Guide for Ministers and Secretaries of State said that ministers were responsible for "the actions of all officials under their management and direction, whether or not the ministers had prior knowledge."

But a version of the guidelines from 2011 says: "Ministerial accountability to Parliament does not mean that a minister is presumed to have knowledge of every matter that occurs within his or her department or portfolio, nor that the minister is necessarily required to accept blame for every matter."

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Mr. Harper insists he did not learn that his former chief of staff, Nigel Wright, wrote a personal cheque for $90,000 to cover Mr. Duffy's expenses until two months after the money was repaid. Mr. Wright and Mr. Duffy are now the subject of an RCMP investigation into fraud, bribery and breach of trust.

Dominic LeBlanc, the Liberal House Leader, said on Wednesday that the changes to the accountability guidelines were meant to insulate the Conservative government. "The Prime Minister wants to set himself up as an accountability bubble boy," Mr. LeBlanc said. "He's trying to ensure that any mess in the apparatus of government, if there is no clear evidence that he himself directed the misdeeds, he can simply wash his hands of it."

Charlie Angus, the ethics critic for the New Democrats, said he does not believe Mr. Harper could use the guidelines to duck responsibility if the criminal allegations are proven, whether he was aware of the scheme or not. "This ministerial code allows ministers to get off the hook if their department screws up, not if a criminal conspiracy is hatched around the minister using the minister's key people," Mr. Angus said.

On Thursday, the Senate's internal economy committee will look into allegations that Conservative Senator Irving Gerstein attempted to interfere in a Deloitte audit of Mr. Duffy's expense claims.

According to RCMP documents, Mr. Duffy's lawyer provided a list of conditions that would have to be met before her client would repay the improperly claimed expenses, including ending the audit.

When Mr. Wright could not find a way to get Deloitte to drop it, the police documents say, he asked Mr. Gerstein to contact the auditors. Mr. Gerstein, in turn, called Michael Runia, a partner at Deloitte. Mr. Runia told Mr. Gerstein the audit would continue, which Mr. Gerstein relayed to the PMO, the documents say.

Neither Mr. Gerstein nor Mr. Runia is expected to testify at the Senate committee, but the senators will hear from Deloitte auditors. "We will be questioning the representatives from Deloitte to make sure that the integrity of the independent audits was never compromised," said Marc Roy, a spokesman for Senator James Cowan, the Liberal Leader in the Senate.

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The RCMP documents also suggest Mr. Gerstein offered to pay Mr. Duffy's expenses from Conservative Party funds when the amount owed was believed to be $32,000. That was called off when the amount hit $90,000.

Liberal Leader Justin Trudeau asked Mr. Harper during Question Period on Wednesday why he still had confidence in Mr. Gerstein, to which Mr. Harper replied that only two people are under investigation – Mr. Duffy and Mr. Wright.

NDP Leader Thomas Mulcair asked if the Prime Minister's code of ethics is the Criminal Code. "In other words, if you're not under criminal investigation by the RCMP, no matter how reprehensible, it's not really wrong?" he asked. "Is that the standard that he's holding his government to?"