As has been mentioned before on this blog, there can be a problem when the power of a country is controlled by too few people and one of those problems is that it becomes easy for the rich to buy political power. This is only one of the many problems of a political system which is controlled by too few people, and to remedy these problems we have democracy. But as we have seen, with a first-past-the-post system, we tend to see the emergence of a small number of parties so the advantages of democracy in sharing power are lost. First-past-the-post is fundamentally undemocratic and so this results in a government which has none of the virtues of democracy, principally being accountable to the people.
If we assume that where the left-right dynamic is concerned that the right-wing party is the party of the rich then it falls to the party of the left to protect the voting public. So then if the right do not mind very much that the fptp voting system tends to favour only a small number of parties, the only chance for the rest of the population to protect itself from government-by-the-rich is the party of the left, in the UK this is the Labour party. If the Tories support fptp then it is unlikely that the rich will buy any change in this policy (since it makes the government easier to buy) and only Labour can do anything about it. As a consequence of this, Labour have a responsibility and an obligation to the voting public to offer an alternative to fptp, they have an obligation to offer and demand proportional representation, or a similarly democratic system which is not fptp. If Labour do not do this they are failing in their obligations as a left-wing party.
