Members of Parliament might feel pressure to toe the party line and maintain party unity in the House of Commons. But a few MPs have stood out for their willingness to rise and vote "Yea" when the rest of their colleagues vote "Nay."

Still, this breaking of the ranks is rare: even the biggest rebel in Parliament votes along party lines 87 per cent of the time.

The "party line" is not always clearcut, and MPs are sometimes given free rein by their parties to vote how they like. For the purposes of this analysis, the party line has been defined as the way in which the prime minister and his cabinet vote (for the Liberals) and the way in which the majority of MPs in an opposition party have voted.

The data was compiled from voting records maintained by openparliament.ca.

In the 198 votes held in the House of Commons — from the beginning of the session in December 2015, through to Feb. 14 — all Liberal MPs have voted the same way 79 per cent of the time. That's a lower level of unanimous voting than any of the other parties in the House.

This is partly due to the prime minister's position on whipped votes. Liberal MPs are only required to vote the party line on election commitments, charter issues and matters of confidence in the government, such as budget bills.

On the other side of the aisle, the Conservatives have all voted unanimously 87 per cent of the time, the New Democrats 95 per cent of the time and the Bloc Québécois 98 per cent of the time.

'Constituents want strong local representation'

Two Liberal backbench MPs are the most frequent dissenters from the party line: Nathaniel Erskine-Smith (22 votes) and Robert-Falcon Ouellette (17 votes).

That represents 13 per cent of all votes cast by Erskine-Smith and nine per cent of Ouellette's voting in the House of Commons.

Nathaniel Erskine-Smith is the MP who has broken party ranks most often in the House of Commons. (Nathaniel Erskine-Smith)

"Constituents want strong local representation," Erskine-Smith said in an interview with CBC News. "Reasonable disagreements are the foundations of democracy."

The Toronto MP says he "consults constituents, evidence and one's own conscience" when deciding how to vote — the only pressures exerted on him, he says, are the personal pressures of being a member of a team.

(Natalie Holdway / CBC News)

When not voting with the rest of his party, Erskine-Smith has most often voted with the New Democrats (18 times) and the Green Party (17), and less often with the Conservatives (nine).

Winnipeg MP Ouellette, who also frequently voted with the Green Party and the NDP, was more likely to vote with the Conservatives (13 out of 17 break-rank votes) than his other frequently dissenting Liberal colleagues.

These included Rob Oliphant (12 votes), Pam Damoff (11) and René Arseneault (10). Still, these three voted with the rest of the Liberal Party at least 94 per cent of the time.

The NDP MP who dissented most often from her party's line was Christine Moore, voting differently from her colleagues three times.

Leadership candidates among Conservative dissenters

The three Conservatives who voted most often against the majority of the party's MPs were Peter Kent (13 times), Michael Chong (12) and Sylvie Boucher (11).

Chong is a candidate for his party's leadership (and Kent has endorsed him). In the last Parliament, he passed a private member's bill, called the Reform Act, to give more power and independence to MPs.

Chong was more likely to vote with the Liberals than the other opposition parties, while Kent voted equally as often with the Liberals, the Green Party and the NDP instead of the majority of Conservative MPs.

"I vote based on the views of my constituents and conservative principles," Chong said in an email.

With the exception of Brad Trost, who has been present for 175 of the 198 votes held through to Feb. 14, Chong is also the leadership candidate who has been most present in the House of Commons.

Contenders Kellie Leitch, Maxime Bernier and Deepak Obhrai have missed the most votes.

When present, Obhrai, who has voted 101 times, dissented with the majority of his party more often than Chong. He voted with the minority of Conservative MPs on eight occasions, representing eight per cent of his votes (Chong's minority votes, meanwhile, represent seven per cent of his total).

Lisa Raitt and Steven Blaney voted with the minority of Conservative MPs on only four occasions, Trost three times, and Bernier twice.

Scheer, Leitch and Erin O'Toole have voted with the majority of Conservative MPs every time they were in the House.

Erin O'Toole, Andrew Scheer and Kellie Leitch have voted with a majority of Conservative MPs throughout this session. (Andrew Vaughan/Canadian Press)

Scheer and O'Toole are among the candidates for the leadership who are aiming to be a consensus second choice for party members — an important factor in a vote that will be decided by a ranked ballot. Chong, however, is running on his party's left flank — which aligns with his voting record in the House.

"I'm running in this leadership race to reduce the power of party leaders, particularly the [Prime Minister's Office], to control MPs," says Chong. "The fight to pass the Reform Act taught me that being party leader is the only way to achieve more ambitious reforms to Parliament and to political parties."

For now, however, all of these dissenting MPs appear destined to remain exceptions to the rule of party discipline in the House of Commons. And that might not be what Canadians want.

In the MyDemocracy.ca survey conducted by the government last year, 83 per cent of respondents agreed that MPs "should always act in the interests of their constituents, even if it means going against their own party."

The survey had been conducted as part of the government's abandoned pledge to reform the electoral system. Considering his independent voting record, it was perhaps fitting that Erskine-Smith then felt compelled to apologize to Canadians for Justin Trudeau's breaking of that particular campaign promise.