PR is essential in a wide, multi-party democratic system. I'm not only in favour of it because UKIP is my party and I want it to do so much better--it simply is a common sense approach to democracy.
Would you disagree?
It's a bit more complicated than that..
PR is a broad term, encompassing many different possible voting systems with their own advantages & disadvantages. Simplest form of PR is the party list system, we have a regional version of this for Euro elections, which means you vote for a party and seats are allocated proportional to the number of votes - but this means the voters have no connection whatsoever to the specific people elected. The party list means that those people "in" with the party at the top of the list cannot be voted out & easily leads to corruption (nearly all corrupt/failing authorities are those where the ruling party believes it will never be voted out, be that local councils, individual MPs or ). Other variants, things like the Additional Member System, which has a FPTP component topped up with a party list in order to get proportionality, have similar sorts of issues.
My favoured system would be STV - the single transferrable vote in multi-member consituencies. Not a fully proportional system, but one that means the electorate get to choose people, and even between candidates from the same party: Conservatives could choose between Eurosceptic and Europhile candidates, for example. It would have a similar, but lower, barrier to entry for new parties compared to FPTP, in that a party would need to get 5th/6th seat rather than win outright in one constituency. Biggest downside to STV is that it expects voters to think a bit more deeply.