OTTAWA -- Not only were Senate expense policies broad, vague and confusing -- now a court is hearing that at least one of them was passed along between administrative staff by word of mouth.

The Senate's top financial official, Nicole Proulx, testified Tuesday that she was told at some point in the past that senators were not allowed to claim travel expenses when they attended partisan fundraisers.

Suspended senator Mike Duffy is facing 31 charges of fraud, bribery and breach of trust, with 18 of them related to travel expenses. In several cases, he was attending Conservative political events.

Duffy's defence lawyer Donald Bayne seized on Proulx's claim that such travel was prohibited. He has taken the court through all of the Senate's guidelines, rules, and travel policies multiple times and hadn't come across that edict.

"Where is that clearly set out? ...There is a man on criminal trial here," Bayne said.

Proulx explained that a colleague told her many years ago that the Senate's internal economy committee had made that decision.

"Where is it written?" Bayne asked.

"It would be a decision. Decisions are in camera, so I would not be able to ... I can't answer that."

Proulx went on to say that the policy was communicated to her by a fellow employee and it predated her arrival in the finance office in the late '90s.

She said she wasn't sure how senators would have been told about it formally.

A list of the kind of events a senator can or cannot travel to on the public dime was finally created in mid-2012, after the period covered by the criminal charges. She says the list was based on the interpretations that were already in place.

The testimony is another example of the Senate's opaque system of deciding important matters of policy within the confines of its standing committee on internal economy, budgets and administration.

The same committee commissioned an audit of the residency status of all senators in late 2012 or 2013 and is now trying to keep it out of the trial.

Also in 2013, the committee asked for legal advice on the constitutional residency requirement of senators, but will not discuss what became of that report.

And that same committee, controlled by the majority Conservatives, worked to redact a final report on Duffy in April 2013 to ensure that it didn't include any negative language about his residency status.

Bayne has focused on the Senate administrative rules, the core document that guides operations and policies in the upper chamber. It specifically includes partisan activities as part of the core parliamentary functions of a senator.