There is a lot of passion for Proportional Representation (PR) at the moment, much of it ill informed.
The argument tends to go something like “First Past The Post (FPTP) is an old, unfair system where people don’t get the result that they voted for. PR is better because it is fair”, there are a number of significant holes in this argument.
Firstly many people talk about PR as if it a voting system, it is not. It is the generic name for a range of voting systems which include three major systems, Party list system in a multi-member constituency, Additional-member system, mixed-member system, Single transferable vote in a multi-member constituency and there are number of variations of system within these including: condorcet methods, Copeland’s method, Kemeny–Young method, Nanson’s method, Schulze method, Bucklin voting, Coombs’ method, Instant-runoff (Alternative Vote), Contingent vote, Borda count, D’Hondt method, Sainte-Laguë method, Hare quota, Droop quota, Imperiali quota, CPO-STV, Schulze STV, etc. etc. I don’t pretend to know or understand half of these and I strongly doubt that most British voters do either.
When it comes to fairness it is difficult to define. One idea of “fair” is that does the political distribution of MPs reflect the political distribution of votes? Another is that the actions of the government reflect the manifesto commitments in proportion to its political composition.
I call the first test the “Who I Wanted” (WIW) test and the second the “What They Promised” (WTP) test. FPTP scores lower on the WIW test than PR systems and PR scores lower on the WTP test because minority parties tend to have disproportionate power when coalition talks take place, often known a the “tail wagging the dog”. This what happened in the London Assembly when Ken Livingstone relied on the Greens to get his budget through, you might be happy with the Greens getting more power than their votes would dictate but would you be so happy if it were the BNP that held the balance of power? Neither system is completely “fair” they are just unfair in different ways.