OTTAWA – When it comes to the Senate expense scandal, more Canadians believe beleaguered Senator Mike Duffy’s story over Prime Minister Stephen Harper’s version of events, according to a new poll.

Some 40 per cent of respondents said they believed Duffy’s tale – including the circumstances surrounding the infamous $90,000 cheque supplied by former chief of staff Nigel Wright – while only 18 per cent think Harper’s telling the truth.

And 37 per cent don’t believe either of them, says the poll from Ekos Research and iPolitics.ca.

“Mr. Duffy, who was in a lot of trouble with the public not long ago, is now seen as considerably more plausible in terms of his position than the Prime Minister of Canada,” said Frank Graves, president of Ekos Research Associates Inc.

“Kind of shocking development, frankly.”

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If it turns out Harper lied or misled Parliament or the public about his role in the scandal more than two-thirds of Canadians think the prime minister should immediately resign, the poll says.

And only a quarter of Canadians approve of the job the prime minister is doing – a historic low for Harper.

“These are scary numbers,” said Graves.

WATCH: Frank Graves, president of Ekos Research, talks about the new numbers for the Conservatives in his poll about Prime Minister Stephen Harper in wake of the Senate expense scandal.

The poll asked respondents whose version of the cheque story they believed: Duffy’s, when he said he was coerced by Harper into accepting the cheque, or Harper’s, who said he was unaware of the cheque and that Wright acted alone.

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It showed that almost all Canadians – at 91 per cent – are paying attention, by following the scandal very closely or somewhat closely.

“The public are pretty close to riveted on this. It’s good circus, good spectacle, and it’s having a dramatic impact,” said Graves.

Harper’s approval now sits at only 24 per cent, with 69 per cent of Canadians disapproving of the way he’s handling his job, the poll says.

WATCH: Tom Clark discusses what Tuesday’s poll numbers mean for the Prime Minister and what Mike Duffy’s latest claims may have on the Conservatives.

That’s half of what NDP leader Tom Mulcair polls, who cleans up with 50 per cent approval, followed by Liberal leader Justin Trudeau at 48 per cent.

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The poll says if a vote were held tomorrow, the Liberals would be in the lead and the Conservatives would be tied for second with the NDP.

The Liberals would take 37 per cent, the Conservatives 26 per cent and the NDP 25 per cent, with the Conservatives down from the 40 per cent support they enjoyed in the 2011 election.

Read more: Conservatives move to shut down expense scandal debate

It appears the Senate expense scandal will have about half of Canadians contemplating it at the polls.

The scandal will mostly impact voters from parties other than the Conservatives, with 54 per cent of NDP voters and 58 per cent of Liberals saying it will affect how they vote, compared to 29 per cent of Conservatives.

Video: Mulcair, Trudeau press Harper over involvement in senate expense scandal

“These numbers are a little scary, and I’m sure they’re not big morale-builders as the government goes into the convention trying to hit a reset button,” said Graves.

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More than half of Canadians also believe the government and country are heading in the wrong direction, at 63 per cent and 52 per cent respectively, compared with 29 per cent and 37 per cent who think it’s going in the right direction.

Support for Senate abolition has in fact decreased since 1994, with 58 per cent of respondents saying they want it abolished immediately, compared to 54 per cent today.

The Senate scandal was seen to be on par with the seriousness of the 2011 robocall scandal, at 75 per cent to 73 per cent, respectively, but slightly higher than the 2004 sponsorship scandal that was considered very serious by 65 per cent of respondents.

The poll was conducted between Oct. 26 to 29, using a unique methodology to randomly contact the public and speak to them online or through live interviews.

The margin of error associated with a sample size of 1,377 is +/- 2.6 percentage points, 19 times out of 20.