IN ONE of his more acerbic comments, the late Pierre Trudeau, a former Canadian prime minister, said that members of parliament were “nobodies” once they were 50 yards from Parliament Hill. These days government backbenchers don’t even have to leave the parliament buildings to fade into the woodwork. They form an appreciative backdrop to ministers during Question Period, nodding and applauding when required. If given a chance to speak, they diligently parrot the party’s talking points. And on all but the most insignificant matters they vote the party line. If they have any original thoughts they keep them to themselves.

Or at least they did until late March, when Mark Warawa, a Conservative MP from British Columbia, tried unsuccessfully to introduce a motion in the House of Commons condemning sex-selective abortion. This was an adventurous move to say the least because Stephen Harper, the Conservative prime minister, had made it known that he did not want the abortion debate reopened. Conservative-dominated committees refused to let Mr Warawa present the motion or to make a statement about it. So he rose on a point of privilege to complain that his rights as an MP had been violated. Amazingly, at least four other Conservative MPs backed him in what was a very public challenge to Mr Harper.

Canadians are not particularly keen consumers of political news, especially of the arcane procedural type. Yet the revolt of the bobbleheads, as Canada’s obediently nodding politicians were labelled by one pundit, made headlines. One reason was that the story concerned abortion, a radioactive subject for the Conservatives because they are suspected of harbouring social-conservative tendencies. But it also highlighted the degree of control exercised by the prime minister’s office, and underlined a fundamental flaw in the political process that has been eroding prime ministerial accountability, and ultimately democracy, since 1919.

The appearance of a handful of dissident government MPs is much more unusual in Canada than in other countries with the Westminster system of parliament, such as Britain and Australia. Mr Trudeau, the former prime minister, is often accused of hastening the slide of MPs into irrelevance by consolidating control in the prime minister’s office. But the slide really began in 1919 when the governing Liberals decided that instead of allowing their MPs to select a party leader, he (and in Canada the leader nearly always is a he) would be chosen at a convention of party members. MPs eventually lost the ability to turf out an underperforming leader.

While the new system is deemed to be more democratic, it has had the opposite effect because it makes MPs accountable to their leader, rather than the reverse. The leader can eject MPs from the parliamentary party or refuse to sign their nomination papers for the next election if they don’t follow instructions. This keeps a tight lid on dissent. In Britain and Australia, where MPs can quite easily get rid of the prime minister, leaders have to keep their MPs happy or face sudden demotion, as Margaret Thatcher and Kevin Rudd both discovered.

Mr Warawa, who has been an MP since 2004, has been around long enough to know the score. So why would he rock the boat? Part of the answer lies in recent electoral history. When the Conservatives formed minority governments in 2006 and 2008 there was a clear need to maintain party discipline, as any musings by rogue MPs had the potential to bring down the government. It was understood that the right-leaning Conservatives could not lean too far right without inviting an attack by the opposition. But once the sought-after majority was won in 2011, the need for discipline vanished: the government was secure until the next election, expected in 2015, and there was less reason for MPs to stay quiet.

Another part of the answer lies in the make-up of the Conservatives. An important sub-section of the party is against abortion and for capital punishment. Mr Harper, whose roots are on the free-market right, has always steered clear of the social-conservative side of things. That hasn’t stopped the opposition parties accusing him of having a hidden agenda, which they claim each time a Conservative MP raises the abortion issue. Mr Warawa’s motion against sex-selective abortion was seen as a disguised way of reopening the broader abortion debate.

The Canadian media jumped on the story because Mr Harper has form in silencing critical voices, not just within his own party but also in the broader bureaucracy. The information commissioner, who oversees access-to-information laws, has just launched an investigation into whether government scientists have been prevented from speaking to journalists about their research. The parliamentary budget officer, whose critical reports frequently embarrassed the government, was not replaced after his term ended on March 25th. The National Roundtable on the Environment and the Economy, an advisory group to the environment minister, was shut down at the end March after recommending one too many times that Canada adopt a carbon tax. Mr Warawa is characterized by some of his supporters as the last in a long line of people with inconvenient opinions who have faced the prime minister’s wrath.

Mr Harper has offered to set up a forum where dissident MPs can air their grievances. Whether that is enough to quell the bobblehead revolt won’t be clear until April 15th, when MPs return from a two-week break. That will also be the first chance for the speaker of the House of Commons to reveal his decision on whether Mr Warawa’s privileges have indeed been violated. The speaker’s position is not an easy one. As a Conservative MP he too depends on the prime minister to sign his nomination papers.