Prime Minister Stephen Harper’s former special counsel and legal adviser worked on the legal deal between Nigel Wright and Sen. Mike Duffy’s lawyer that called for Wright to help Duffy pay off $90,000 in invalid expense claims, CTV News has learned.

Sources told CTV’s Ottawa Bureau Chief Robert Fife that back in February, Benjamin Perrin helped draft the letter of understanding that called for Duffy to publicly declare that he would repay the money. In return, sources say, Wright would give a personal cheque to Duffy to cover the $90,000. Sources say the agreement also stipulated that a Senate investigation into expense claims would go easy on Duffy.

The Prime Minister’s Office insists that neither Perrin nor Wright told Harper about the payout to Duffy or about any aspects of the secret arrangement.

The PMO also declined to release the letter of agreement, saying it is now in the hands of Ethics Commissioner Mary Dawson, who is investigating Wright’s $90,000 cheque to Duffy.

Dawson’s investigation could take a year or more.

Attempts to reach Perrin via email and telephone last week and on Monday were unsuccessful.

Perrin left the Prime Minister’s Office in April and has returned to his position as an associate professor at the University of British Columbia’s Faculty of Law.

According to Perrin’s online biography on the UBC website, while in Ottawa he served as a lead policy adviser on matters related to the Department of Justice, Public Safety Canada and Citizenship and Immigration Canada. He is a renowned expert on human trafficking and child exploitation.

On Sunday, Wright resigned as Harper’s chief of staff, saying that he did not advise the prime minister of the “means by which Sen. Duffy’s expenses were repaid, either before or after the fact.”

Harper said in a statement Sunday that he accepted Wright’s resignation with “great regret” and thanked his top aide for his contributions to the Tory government.

“I accept that Nigel believed he was acting in the public interest, but I understand the decision he has taken to resign.”

Duffy’s expenses had been the subject of an internal audit, along with those of Senators Patrick Brazeau and Mac Harb.

Under the Senate’s housing rule allowance, senators can be compensated for living expenses if they live more than 100 kilometres from Ottawa, requiring them to maintain a secondary residence.

However, evidence outlined in an independent audit showed that Duffy, Brazeau and Harb each spent more time in the capital than at the homes declared to be their primary residences, rendering their claims ineligible.

Earlier this month, a Senate committee ordered Brazeau to repay about $48,000, and Harb $51,000.

Brazeau insists that he didn’t break rules by claiming the housing allowance, and he is determining if the order to repay the money can be overturned. Harb has retained a lawyer and will attempt to “quash” the audit’s findings.

Fife reported Monday night that, “A lot of Conservative MPs would like to see the Conservatives use their majority in the Senate to strip the pay and benefits of Duffy, Pamela Wallin, Patrick Brazeau and Mac Harb. It’s a question that will be put to the prime minister tomorrow by Conservative MPs, I suspect, and certainly by the media.”

On Tuesday morning, Harper will hold a meeting with Conservative MPs and senators, many overwhelmed by complaints from constituents about the issues raised in recent weeks.

“Conservative MPs are going to be seeking answers. They’re getting an earful from their constituents about this, but I’m afraid they’re not going to be very happy with the answer,” Fife said. “The prime minister’s version is that he was in the dark and that he didn’t know and he’s going to tell his caucus if anybody else is caught fleecing taxpayers, they are going to get the boot.”