Apparently I'm all wet! (12 May 2005)
What Adam seems to be considering is only a pure party-list system, in which there is no geographic representation at all, but thats not the only kind. In fact, under either an Additional Member System or Mixed Member System (from the copy of the Voting Systems FAQ that I've been hosting for two years), the exact balance between geographically-elected and “at” large candidates can be set anywhere from one extreme to the other just by adjusting the number of representatives selected each way. If the "my local representative works for me" dynamic is weaker under such a system, its by design.
When people shout “proportional representation”, that's what they mean around here. I didn't mean to suggest that other systems with proportional elements don't exist, but even in those systems my concerns still stand (to a greater or lesser extent, depending on the degree of proportionality).
Proportional representation is not a way to select MPs, it's a way to select parties. In a proportional vote you really might as well give the parties block votes and save the effort. Debates may be held, but a party has made its mind up by the time the bill reaches the house. (The quality of Commons debates is usually pretty bad as well.)
That brings me to a more general kind of question about arguments like Adams. Why is geographic representation considered so important anyway?
Geographic selection is much less useful and less needed now than ever before. But it still gets us a specific representative for each person in the country. (As you can guess, I quite like that.) I think there should be more feedback for a legislature than a single vote once every five years. I just don't see that a letter to "party headquarters" is the same. (Maybe I'm fooling myself in thinking that writing to an MP makes any more difference at the moment.)
So maybe we would be better off without a geographical basis. Let people vote for a single party and give that party voting power equal to number of votes/total number of voters. The party can then use their fraction to vote in a representative manner (possibly with internal voting procedures). We could all vote for the "Freedom loving geek party" and be happily represented.
(In fact, if a party were allowed to split their fraction into "yes" and "no" parts we could vote for a direct democracy party which would let its members vote on each and every decision and split the party vote accordingly. Direct democracy worries me because a great many of my fellow countrymen are really stupid. Several years ago I'm sure that a popular vote would have introduced the death penality for pediatricians, such was the public concern about pedophiles.)
This also leaves open the question of how the executive is selected. At the moment it's the leader of the biggest party (well, actually, it's up to the Queen, but she's pretty predictable). With a proportional system may well need to directly elect the executive too. Condorcet anyone?
But I'm unsure about proscribing such a change because there are likely to be lots of emergent effects. Thus my support for a fairly modest change (to approval voting) at first.