As for what I don't understand... in Americaland... we have pre-determined cylical elections. We'll have a presidential election in 2012. The next one in 2016. The next one in 2020. The next one in 2024. There's a VERY EASY TO DETECT pattern there.
Here's a list of British Elections from 1920-1960: 1922, 1923, 1924, 1929, 1931, 1935, 1945, 1950, 1951, 1955, 1959.
What the hell?
Now I know you guys don't directly elect your Prime Minister. I'm not as stupid as the American stereotype. I also know that Prime Ministers can change without an election (Churchill famously took over on the same day Germany invaded France... PERFECT TIMING in my book). I've got no doubt that it's due to what I grew up with, but to me, it seems that having scheduled elections is a much, much better idea than elections on a whim. Elections on a whim seems to reward populism (Newt taking over for Clinton or Sarah Palin taking over from Obama now), and if you look at the majority of parliamentary systems around the world, I'd say the evidence backs up my opinion (Italy, Thailand, Japan, most of Eastern Europe, again post-Soviet Russia, which I won't even PRETEND to understand, etc). As much as I despise American gridlock, I'll take gridlock over populism any friggin day.
Also... kudos to Britain for "doing it right". There's a fine (sometimes... sometimes it's very, very obvious) line between democracy and populism. You guys rarely cross it. I salute you for that.
As I understand it elections are held at the behest of the sitting government, within a limited time frame. There's a set number of years after which there must be a general election, but the sitting government can choose to hold one earlier and frequently do if they think they'll win. If they think they'll be voted out they delay as long as possible.
Bearing in mind that the sitting government is determined solely by the number of seats each party has in the House of Commons. The prime minister is the leader of the majority party, as you say he's not elected to that post except by the internal election of his party. The government ministers are appointed by the prime minister. All of which requires the Royal assent. A party, no matter how many seats it has in Parliament, may not form a government without the Sovereign's permission, nor may a coalition of parties. Parliament may not convene without the Soveriegn's permission nor may a Bill passed by the Commons and the Lords become law without the Royal assent. An election may be held but Parliament cannot be dissolved without the Soveriegn's permission. In fact, the sitting prime minister has to physically go to the palace and ask the Sovereign to dissolve Parliament in order for a new one to be elected, and the Soveriegn must then formally open Parliament again.
I'm just praying for the day when Parliament is dissolved and permission to form a new one is witheld. That'd be sweet.
It's a comparative thing. And I wasn't comparing it to US government (tho, seriously, look at us), I was comparing it to other parliamentary states. Like... France... Russia... Italy... etc, etc, etc.