The expenses of every single senator sitting in the upper chamber may be scrutinized by Canada’s auditor general as his office begins a thorough review of the Senate.

Auditor General Michael Ferguson said he’s still very much in the early stages of an unprecedented study of Senate expenses, which was sparked by external audits of housing and living allowance claims by three senators -- Mike Duffy, Patrick Brazeau and Mac Harb -- and the travel expenses of Pamela Wallin.

Ferguson appeared before the Senate Internal Economy committee Tuesday evening, as one of the first steps in the audit process.

Following the meeting, Ferguson told reporters in Ottawa that he hasn’t determined whether a sample of senators will be looked at in the audit, or if his office will examine the expenses of everyone.

“We still have to determine exactly what we’re going to look at, the whole scope of what we have to deal with,” he said. “But certainly one of the things we will focus on is individual Senate claims.

“We will have to look at things like how long it will take to look at every single senator, how many claims are there, how far back we would go,” he continued.

Ferguson wouldn’t speculate on how long the audit would last, but said most performance audits take an average of 18 months.

During that time, Ferguson said he expects to have unrestricted access to pertinent information.

“We will set what we want to look at and we don’t expect there will be any restraints on the work we want to do,” he said. “Our understanding is there will not be any restrictions on what we want to do.”

Ferguson acknowledged the heightened public interest currently surrounding the Senate and said his office may provide some sort of interim audit partway through the process.

“We’re not going to conduct all our steps in public,” he said. “The next time we will say anything on this is when we are tabling the report.”

Ferguson’s appearance before the Internal Economy committee came the same day as its chairman, Sen. David Tkachuk, announced he would be stepping down as he prepares to undergo preventative treatment for cancer.

Tkachuk, who was appointed to the Senate in 1993 by Brian Mulroney, has chaired the committee since 2011. He is stepping down as of Thursday.

“Because treatment will take me through the summer (and) there’s no guarantee of success, it makes it impossible for me to fulfill my duties in these very trying times,” he said Tuesday in the Senate. “It is in the best interest of the committee and of the Senate that I step down as chair, though I will remain as a member the committee.”

The committee, which oversees the financial administration of the upper chamber, has been at the centre of a growing expense scandal.

Last month, the committee released reports based on the independent audits of housing expense claims filed by Duffy, Brazeau and Harb. Senators are entitled to a housing allowance if their primary residence is more than 100 kilometres outside of Ottawa.

The committee ordered Harb to repay about $51,000 and Brazeau about $48,000 in ineligible expenses. Both men are fighting the orders, with Brazeau arguing that his audit concluded he met the four indicators required for primary residence claims.

Duffy repaid about $90,000 in expenses in March, before the results of his audit were made public. In May, Sen. Leader Marjory LeBreton said she considered the matter closed.

However, CTV News reported that Duffy received $90,000 to make that repayment from Prime Minister Stephen Harper’s Chief of Staff, Nigel Wright. Days later, Wright resigned and Harper has maintained that he knew nothing of the deal until the CTV report aired on May 14 and Wright confirmed the deal the following morning.

The opposition parties have hammered the Conservative government over who in the Prime Minister’s Office knew about the agreement.

CTV’s Ottawa Bureau Chief Robert Fife also reported that Tkachuk and Sen. Carolyn Stewart Olsen, also a member of the internal economy committee, ordered that damning language in Duffy’s audit report be removed, including the fact that Duffy refused to co-operate with the auditors. Tkachuk has denied that the report was whitewashed in any way.

When the audits were released in May, auditing firm Deloitte requested extra time to review Wallin’s travel expenses. The extension was granted and the results of that audit are expected sometime this summer.

Last week, Fife reported that Wallin has already repaid $38,000 in travel expenses she claimed over the past 19 months, and could have to pay back an additional $20,000.