Iain Dale looks at the hurdles would-be MPs must overcome just to get their names on a ballot paper.

It comes as no surprise that most MPs have the hide of a rhinoceros and a highly developed ego. After all, if they've survived the candidate selection process they should be ready to face anything that a political career can throw at them.

Becoming an approved candidate for the two main parties has always been the political equivalent of completing a 100-yard obstacle course but now even the Liberal Democrats don't let just anybody stand.

Not that long ago the mere act of joining the Liberal party was qualification enough to be asked to stand for parliament. These days even power-hungry party members have to submit themselves to a series of interviews before they are added to the nationally approved candidates list and are allowed to start persuading a constituency to adopt them as a local candidate.

But this is nothing to the torment up and coming Tories have to contend with. The forms they fill in ask for the most minute details about a candidate's work and private life and only just stop short of asking for an inside leg measurement. The weekend away at a hotel is an endurance test which the SAS would be proud of.

And yet despite the oddballs still get through. It is perhaps best not to speculate on what the failed ones were like.

After the hotel test, central office leaves the rest of the selection process to local parties, although there are strong rumours that they are about to follow Labour and impose candidates in important byelections.

Following the Greenwich debacle in 1985 - when the far left Labour candidate Deirdre Wood lost the seat to the SDP's fragrant Rosie Barnes - Neil Kinnock vowed never to let it happen again and set in train a series of reforms in which Labour's national executive would control the shortlist of candidates for the local party to choose from.

But even this is not guaranteed to avoid controversy, as Labour found out this week in Ogmore, where national executive member and Tribune editor Mark Seddon failed to make the final cut.

The Labour party chairman, Charles Clarke, said it had nothing to do withMr Seddon's persistent criticism of New Labour or with the fact that Mr Clarke himself only just beat Mr Seddon to the Labour nomination for Norwich South after a bitter contest in 1997. Yeah, right.

The more interesting fact about the Ogmore selection is that only 38 Labour aspirants bothered to apply for what is a safe seat. If this had been a Tory safe seat - assuming such a thing still exists - there would have been several hundred applicants. Presumably only 38 poor souls felt they would make it past the Millbank Thought Police.

Although the Lib Dems cannot impose a candidate in a byelection they do insist that all shortlisted candidates are grilled by a panel to test whether they are up to facing the most gruelling three weeks of their lives.

If they fail they have to withdraw from the process.

Among Conservatives there is even talk of bringing in psychometric testing. A more radical move would be to actively seek out candidates who are not necessarily even party members but who offer something more than the usual white, middle class ex-party headquarters apparatchik identikit Tory candidate.

But until the Tories address the problem of their ageing membership they are highly unlikely to attract more women, gay and ethnic minority candidates as the local associations just won't choose them. And let's face it, if you were a 40-year-old woman with a proven successful track record in your career, would you really bother to continue if you had been through 30 or 40 candidate selections, only to fall at the final fence every time?

Being asked "does your husband know you're here?" and having to grit your teeth and give a smiling answer is a pleasure most women would be happy to forego.

When a local Tory association in a safe seat selects an openly gay candidate, we'll know that progress is being made. But don't bet on it happening soon.

For a federal party the Lib Dem system is surprisingly centralised. In the party it is not possible to stand for parliament unless you are on the approved list. Tories have the scope to apply for their local constituencies even if they are not nationally approved.

Liberal Democrats too have to attend what is delightfully termed a "development weekend", which is the political equivalent of taking a GCSE.

No one fails. Instead you are graded from 1 to 4, with grade 4 being "you have many qualities but we think you can be more valuable to the party in other roles". Translation: carry on delivering those Focus newsletters and don't bother us again.

The Tories go for a "pass or fail" approach, which although on the face of it is more honest, can lead to festering grudges among those who fail and might have been loyal party workers for years.

All this might be about to change. The Electoral Reform Society has a commission, chaired by Peter Riddell of the Times, looking at the issue of candidate selection in all the parties. It reports in the autumn.

It is difficult to see how it can recommend a common system for use by all three political parties because each party is constrained by its members on how far it can change. And this is the root of the problem. Unless all three parties address the problem of falling and ageing membership it is difficult to see how better quality candidates can come through the system.