OTTAWA (AFP) - Canada's Senate on Tuesday effectively expelled three of their own for what an audit revealed were "troubling" expense claims, as a federal police probe intensified.

Senators Mike Duffy, Pamela Wallin and Patrick Brazeau - all of whom were appointed by Prime Minister Stephen Harper - were stripped of their duties, staff and salaries for two years.

But they will keep their health and other benefits.

The trio were accused of charging hundreds of thousands of dollars for travel and housing expenses in a scandal that has been a drag on the ruling Conservatives' popularity - now at an all-time low, according to polls.

Brazeau also faces criminal charges for alleged domestic violence.

Duffy meanwhile is also being investigated for having accepted a C$90,000 (S$107,200) check from Mr Harper's chief of staff to help the lawmaker repay funds he had wrongly claimed as Senate expenses.

Mr Harper's right-hand man, Nigel Wright, resigned in May after revealing the payment.

Duffy has alleged that the prime minister's office was behind a cover-up to try to quell the uproar, "to make a political situation embarrassing to (Harper's) base go away".

He alluded to emails detailing negotiations between his, the prime minister's and the Tory party's lawyers over the scheme, showing "back and forth as the PMO lawyers check with their principle on the language that would be used to direct the future actions of Senator (Marjorie) LeBreton (Tory Senate leader) and others in the Conservative party leadership" to go along with the plan.

As part of the scheme, Duffy said he was told to respond, if asked by reporters where he got the C$90,000 to repay the Senate, that he took out a bank loan, that it was part of a "script" written for him by the prime minister's office.

"When the media ask, where did you get the money to pay the C$90,000 the PMO told me to say, 'My wife and I took out a loan at the Royal Bank," Duffy said.

"That line was written by the PMO to deceive Canadians as to the real source of the C$90,000."

Duffy's scathing attack on his former boss and own party prompted the Royal Canadian Mounted Police (RCMP) to ask him to hand over any "emails and documents which may be material to our criminal investigation," according to a letter from investigators released by the Senate.

"The existence of such documentation may potentially be evidence of criminal wrongdoing by others," wrote RCMP Superintendent Biage Carrese.

Mr Harper has steadfastly rejected a barrage of questions about what he knew and attempts to link him directly to the scandal, while pushing for suspending the three senators.

"You cannot claim an expense you did not incur. That is not right, that is not proper and that will not be tolerated in this party," Mr Harper has said.

"Removing these three Senators from the public payroll was the right thing to do. These Senators have been found by auditors to have claimed inappropriate expenses. They should not be collecting a public paycheque," his spokesman Jason MacDonald said after the vote.

The only senator of the group to speak after the vote, Wallin lamented a "flawed" process led to her ouster, and added: "It's an extremely sad day for democracy."