Main arguments against First Past the Post
One argument against First Past the Post is that it does not give a fair result of voters view. Most MPs are elected with less than half the votes in their Constituency and in most cases more people vote against the winning candidate than for them. For example In 2010, 62% of voters did NOT vote for David Mundell in his Constituency. This means over half of the voters are saying they would prefer someone else. This is not fair or representative.
The system leads to thousands of wasted votes since voting is not proportional. Only the votes cast for the winning candidate count. All of the rest are worth nothing. Usually more people vote against the winning party or MP than for it. This can lead to voter apathy - when people can't be bothered to vote when they don't think their vote matters which is not good for democracy.
It does not always deliver a decisive victory for one party and create a strong stable government. The Conservatives failed to win an overall majority in 2010 in the general election. They formed a coalition with the Liberal Democrats but the parties disagree about major issues like university fees, welfare reforms and reform of the house of lords which makes governing and passing laws harder.
Third parties are penalised. The system upholds the existence of a 2 party system and so is biased in favour of the major parties and this is not democratic. It is unfair to smaller parties such as SNP ( Scottish National Party) or Liberal Democrats whose support is spread across the UK but is not concentrated(big) in particular regions. This makes it hard for them in one constituency to get enough votes to beat larger parties. For example in 2010 Liberal democrats won 23% of the votes, but only got 57 seats. Proportional representation would be fairer to small parties as the % of vote they won would be the same % of seats they won.
It encourages tactical voting, as voters vote not for the candidate they most prefer, but against the candidate they most dislike.
Geography decides whether your vote will make a difference. FPTP encourages safe seats In safe seats one party has such a popular majority that it would take 1000s of voters to change their mind to alter the predicted outcome. All of Glasgow's constituencies are held by Labour and Conservatives do badly in these. Why should a Conservative voter bother to vote if their vote won't count. With Proportional Representation their vote would still count. Voters in marginal seats have more chance of influencing which party becomes the government than voters in safe seat.
Example Safe seat Richmond (Yorkshire) 2010. Conservative ( William Hague) over 33,000 with second rival at 10,000.
Voters in safe and super safe seats tend to be ignored and this is not good for democracy and can lead to voter apathy. In these constituents the winners know they will win and therefore do not spend time and money listening to the views of the voters who live there. The losing party might run a small ‘token gesture’ campaign, they don’t put in as much effort and might give an inexperienced candidate in it. After the election there is little motivation for the MP to work hard for constituents, instead it can be more important that the MP pleases their party to be re-selected for a safe seat.