D
Deleted member 231381
Unconfirmed Member
As far as the UK is concerned, the process of becoming an official party candidate varies by party. For the Conservative Party (think right wing of the Democrats or maybe Jon Huntsman Republicans), you send an application to the Conservative Party headquarters where your candidacy is approved, and then if there are multiple candidates for a position, then a vote is usually held among the local party branch, which is the equivalent of caucus insofar as that you have to actually turn up to the party branch meeting in question and be a member of the party. Labour's (leftwing of the Democrats plus an aspect more left than you can find in American politics) is more or less the same, except Labour's control over candidate approval is weaker.
To become the leader of the party and ergo the candidate for Prime Minister is again at the discretion of these parties. In the Conservative Party, you have to be a sitting Conservative MP or member of the House of Lords, although in practice no member of the Lords ever runs in the modern era, and submit your candidacy. Sitting Conservative MPs then have successive knock-out rounds where the weakest candidate is eliminated and a second round of voting occurs, until only two candidates are left. This is then open to a general vote to Conservative party members, a little like a closed primary except all the voting is done by post (or increasingly online).
For Labour, you have to be a sitting Labour MP, and submit your candidacy with the endorsement of at least 15% of the current sitting Labour MPs. After that point, anyone who is a Labour member or chooses to affiliate with Labour can vote in an alternative-vote election, equivalent to a US semi-open primary but with a different (better) voting system. Again, voting mostly occurs by post.
As far as the UK is concerned, the Labour leadership process is probably more open than both of the equivalent US parties (insofar as that there are no superdelegates, there is a single election with everyone's vote counting for the same, and it is not closed, although there is a £3/$5 charge associated with affiliation), and the Conservative leadership process is more closed, given that they get to chose between the two candidates most favoured by the Conservative establishment.
There are some key differences between parliamentary parties and the US ones, though. Firstly, in most parliamentary countries, parties' private affairs are entirely self-funded. You can't claim public funds for running private elections, the way US parties do. The second is that most parliamentary countries that aren't Anglo-Saxon in heritage have far more competitive electoral systems than the US that support multiple parties. If you don't like the leader of a given party, you can vote for an alternative party on the same side of the political spectrum and that has a meaningful impact. In the US, the electoral system is set up in such a way (first past the post, presidential executive, federalist) that essentially only two parties can ever exist; US parties are almost organs of the state whereas parliamentary parties often come and go and are susceptible to a much more competitive arena. I think the fact that firstly US parties demand public funding and secondly the Republicans and Democrats between them have effectively turned the US electoral system into an electoral cartel means that, as a matter of democracy, primaries ought to be semi-open (i.e., open to people who registered as party X or did not register for any other party).
Really, though, America ought to change its electoral system full stop. The alternative vote would be a good start.