It is crunch time for Labour's all-women shortlists. Today an industrial tribunal will begin to consider the case brought by two spurned parliamentary hopefuls, Peter Jepson and Roger Dyas-Elliott. Rejected by constituencies on the grounds of their gender, they are claiming that the party is guilty of illegal sex discrimination.

The Labour Party's aims are worthy enough. It is rightly determined to increase the number of women at Westminster. Out of 271 Labour MPs, only 39 are women - yet politicians make decisions which affect the whole population, more than half of whom are female. In its pursuit of a better gender balance, Labour is prepared to risk excluding brilliant men from Parliament this time round while at the same time stamping on some fragile male egos.

Cynics might suspect Mr Jepson and Mr Dyas-Elliott of bringing their case simply out of pique and disappointed ambition. After all, their budding careers as bright backbenchers under a Tony Blair government have been blighted. However, on the face of it they seem to have a pretty strong case. All-women shortlists mean some people will not get the chance to stand for Parliament in their home towns, effectively because their genitals are the wrong shape. It sounds like an outrageous and unfair thing to happen.

If a company today refuses to consider people for jobs purely because they are men, then it is guilty of breaking the law. A climate of discrimination against women that stretches back centuries is not enough to justify denying equal employment opportunities to individual men. However, the Labour Party will try to convince the tribunal that the selection and endorsement of MPs is significantly different from the normal process of appointing people to jobs.

Clearly there is some truth in what it says. Selecting prospective politicians is not like interviewing job applicants. The process is deeply flawed and prejudiced. A quick glance across the back benches is enough to convince anyone that male Labour MPs are not always chosen on the basis of outstanding talent.

Things are not much different in other parties. Local Conservative associations mostly decide to plump for men rather than women, and for married men rather than single men, when choosing new candidates for safe seats. It is implausible that in every case the married man just happens to be the best candidate. It is far more likely that those with the power to choose simply prefer married candidates - either because they consider a wedding ring makes you better able to do the job or because they think the voters will like it better.

In the end it is the voters who will decide. If the electorate really does want more women in Parliament, that is eventually what they will get. Conservative Central Office is rumoured to be contemplating its own form of positive discrimination for women after the next election, because it realises how important the issue has become. Political parties must provide the candidates the electorate wants, or they will die.