Senator Mike Duffy is listed as being on Senate business during the last federal election on two days when documents show he was campaigning for the Conservatives in the Greater Toronto Area.

The Deloitte audit that reviewed the living and travel expense claims for Duffy and Senators Mac Harb and Patrick Brazeau shows that Duffy was neither in Ottawa nor Prince Edward Island, but in an "other location" on Senate business on April 27 and 28, 2011.

The prime minister's office said Thursday the Conservative Party is reviewing Duffy's expense claims from the 2011 campaign.

He remains a Conservative senator, but he is under increasing internal party pressure to leave caucus.

Senate rules allow for the work of senators to continue during elections. It is not known what Senate business Duffy was conducting on April 28.

Duffy did not co-operate with the Deloitte auditors. The report says it is not clear from his travel claims where he was on the days he claimed per diem amounts.

But an invoice written by Duffy is titled, "Mike Duffy campaigning in the GTA, April 27 & 28, 2011." It indicates he flew out of Ottawa on April 27, spent the night in a hotel in Toronto on April 28, and flew back to Ottawa on April 29.

The invoice is included in Elections Canada campaign expense records for Natural Resources Minister Joe Oliver's campaign. Oliver was elected in the Toronto riding of Eglinton-Lawrence.

An email from a political operations officer for the Conservative Party of Canada, Felix Wong, to Oliver's campaign manager, John Penner, is also in the expense file. It says the total cost for Duffy's trip to Toronto was $1,355.56 and "that amount will be divided between the eight ridings that he visited, so each riding will be responsible for $169.45."

Campaigns reimbursed Duffy for visit

Wong writes that Oliver's campaign "will have to reimburse the senator directly."

Penner then writes Larry Babins, the official financial agent for Oliver, saying the campaign was never told it would have to pick up the tab for Duffy's appearance, "but guess we're on the hook for 170 bucks."

The NDP circulated this poster during the 2011 election campaign, objecting to partisan campaigning by Conservative senators. (CBC)

Duffy spent several other days campaigning that month but the audit shows he was on Senate business. The Canadian Press reported other instances where Duffy also billed campaigns for the expenses.

On April 21, for example, Duffy was reportedly campaigning with Scott Armstrong in Nova Scotia and his campaign paid Duffy $409.91. On April 8, it appears he was in Norman Wells, N.W.T., with Sandy Lee, whose campaign paid him $209.91 in expenses for the trip.

The audit also determined that Duffy filed per diem claims while he was in Florida for 12 days. Duffy repaid $1,050.60 and said it was a "clerical error" that those claims were made.

The audit of the three senators looked at travel claims and the living allowance that senators can claim to stay in Ottawa if their primary residence is more than 100 kilometres away. Duffy, a former journalist, has a longtime home in Ottawa and a residence in Prince Edward Island. The living allowance is worth up to $22,000 a year. The audits were trying to determine whether the senators were properly claiming the allowance.

Contradictory explanations

Before the audit was completed, Duffy said he would pay taxpayers back for $90,172 but that he hadn't done anything wrong. He said the forms where senators declare where their primary residence is are confusing. The audit said the rules need clarification.

On Wednesday, Prime Minister Stephen Harper's office revealed that Harper's chief of staff, Nigel Wright, gave a certified cheque from his personal account as a gift for the purpose of covering the repayment.

The date on Wright's cheque is not known.

CTV News reported Wednesday that Duffy had previously told them Wright had nothing to do with his repayment.

That would not be the first apparent contradiction in Duffy's response to the controversy.

During an interview with CBC News in Charlottetown on Feb. 22, Duffy said that he and his wife were going to "voluntarily pay back my living expenses related to the house we have in Ottawa."

On April 18, he told Global News that he was waiting for the results of the audit before deciding whether he would make a repayment.

The next day, he issued a statement saying the money had been repaid.

P.E.I. Liberal MP Wayne Easter called on Duffy to resign, saying that the gift from Wright "would just suggest that somebody is now bought and paid for."

"A senator is supposed to be independent of the politics of the prime minister's office. A senator is supposed to represent his region, take the prime minister's office on when you have to," Easter said.

Stumping senators

Duffy wasn't the only Conservative senator helping out Tory candidates during the 2011 election.

Last February, the NDP said Pamela Wallin charged taxpayers nearly $26,000 in travel expenses while appearing at a series of Conservative campaign events.

NDP MP Olivia Chow said Thursday that one of the campaign events Duffy attended was in her Toronto riding.

"He was supporting the local Conservative candidate and on top of that, he was claiming Senate expenses while he was actually campaigning," Chow said.

"Conservatives and Liberals are using the Senate to reward their friends and then on top of that, using these senators to fundraise and do partisan activities while claiming taxpayers' money. And that's just a complete abuse," she said.

"It's up to the prime minister, but the prime minister always said: done the crime, do the time. And so far, there [are] absolutely no consequences at all when you are caught cheating taxpayers' money," the Toronto MP said.