The findings threatened to erode what little regard Canadians still have for the country’s unelected and unloved Senate, which was already under a cloud from a highly publicized fraud and corruption trial of one member that started in early April.

Though the body has little practical influence, the audit of its spending practices, prompted by that case, promised to make significant political trouble for the Conservative government of Prime Minister Stephen Harper, not least because several of the most prominent senators involved are his appointees, with close ties to his party.

And some senators did the chamber few favors with their complaints during the audit process. One Conservative member, Nancy Ruth, became indignant that auditors challenged a claim she made for the cost of breakfast after traveling, complaining that they expected her to be satisfied with the “cold Camembert with broken crackers” she was offered on her flight. She got no sympathy.

The auditors said on Tuesday that the issues they had found were systemic, and not just isolated slip-ups. “The weaknesses and problems uncovered in the course of this comprehensive audit of senators’ expenses call for a transformational change in the way expenses are claimed, managed, controlled and reviewed,” the audit report said. “Simply changing or adding to existing rules will not be enough.”

The Senate was set up in the 19th century in part to protect the interests of landowners, but it has come to be widely seen as an ineffectual institution whose chief purpose is providing patronage posts. Canada was not even 10 years old when the first calls were made to overhaul it. But successive governments have proved unwilling or unable either to tackle the job or to put the Senate out of its misery, with Mr. Harper the most recent.