But in the US they tend only to use FPTP.
"The first past the post system is justified because it places responsibility for government in the hands of a single party. It's used in the United States, where the president can be described as representing all the people, even if he has won less than half the vote[ CITATION Gab07 l 2057 ]". In both countries there has been argument that the FPTP isn't a good fair way of voting because the winner could actually have more people vote against him/her than the amount of people voting with him/her. Some people want to go by the Party List-PR system of voting but FPTP is a cheaper way and more efficient way of voting as it is easy to count the votes and it has little room for extremists. "The debate however between FPTP and PR is thus very much about which values should get priority. But the debates isn't solely on values. Interests also matter. Some parties are bound to do better in one party system than the other: first past the post tends to benefit larger parties and PR smaller ones[ CITATION And08 l 2057 ]". In my view I think the US and the UK are using the correct system due to large population and larger parties.
There aren't just positives to this system however, it also has cons. In both countries the FPTP excludes small parties because the smaller ones aren't getting a say. In the US there are the two main parties, the Democratic Party and the Republican Party however the Independent political party is excluded because people voting will tend to vote for the bigger more known parties than the small parties. This is a major issue and if there was a PR system people would be able to give the independents their second or third votes meaning they wouldn't be so excluded. It's the same in the UK however, the Conservatives, Labour and Liberal Democrats are the main parties in the UK leaving the other small parties out.