For the next two weeks all political eyes will be on Eastleigh, a suburban seat on the outskirts of Southampton abruptly vacated on February 5th by Chris Huhne, a scandal-plagued MP. The by-election deliciously pits the Conservative Party against the Liberal Democrats; opportunities for coalition-straining rows abound. But Eastleigh gives a false impression of British politics. More than two-thirds of seats in the House of Commons are safe. Landing the right party ticket in one is to become an MP-in-waiting. Around the country, the 2015 parliament is quietly taking shape.

Would-be Conservative MPs attend a Parliamentary Assessment Board (PAB) where they complete five exercises: public speaking, an interview, an in-tray test (in which candidates must speedily prioritise and complete a series of desk-based tasks), a group exercise and a written exam. The process is designed to uncover brainy, personable Stakhanovites with steely resilience and the gift of the gab. Peter Botting, a consultant who trains prospective candidates, describes one pupil who is used to working long hours but was “shattered” after the six-hour assessment.

Critics say the process disadvantages outsiders who lack relevant political or professional experience. But Jo Silvester, an organisational psychologist who helped the party draw up the tests, counters that it weeds out substandard candidates, including ones with desirable backgrounds. Only once a hopeful has proven his abilities is he free to apply for seats, schmooze local members and bid for their votes at selection hustings.

The Lib Dems also screen applicants before letting local activists pass judgment. But whereas the Tories are looking for future Commons stars, their coalition partners are interested in campaigning grit. Although the Lib Dem assessment is based on the PAB, it tests for two other skills: “representing people” and “values in action”. These, says a senior party figure, reflect an expectation that candidates should make a “huge personal commitment” to their constituencies. The party has few safe seats, so a strong local following is essential. Mike Thornton, the party’s new candidate inEastleigh, epitomises the type. A veteran of 20 years of leafleting and a councillor of five years’ standing, he admits that running for election “has been an ambition for some time”.

Once singularly control-freakish, in 2011 the Labour Party dropped its multi-stage pre-screening process and allowed aspirants to apply directly to stand for individual seats. Labour’s general secretary, Iain McNicol, is watching the new batch of selectees cautiously, but declares himself satisfied with the quality of candidates. “All power to the members”, he proclaims, noting that the process favours a certain type of candidate, one who can organise neighbours to battle library closures, high street loan sharks, antisocial behaviour and the like. Such activities, says Mr McNicol, underpin “everything we will do” in the run-up to the 2015 election.

But there is a limit to how much party machines can control their intake. Before the last election the Conservatives gave priority to an “A-list” of prospective candidates deemed politically desirable for their glamour, youth, professional success, sex or ethnicity. Sure enough, the independent-minded 2010 intake contains few grey party drones. It has also proved head-bangingly unruly and virtually unleadable. Party leaders should be careful what they wish for.