Voting reform: The referendum explained

Under first past the post, voters choose one candidate, and the person with the most votes wins.

Supporters say it creates strong governments because coalitions are less likely, it is fair because one person gets one vote and it is easy to understand and implement.

However critics say it is unfair because two thirds of MPs are elected with less than 50 per cent of voters supporting them, a small number of voters in marginal constituencies decide the outcome of elections and say voters in safe seats are given little incentive to cast their ballot. They also point out that the 2010 result shows even first past the post can deliver hung parliaments.

Under the alternative vote, people can rank candidates in order of preference – one, two, three, four and so on.

The winner is the first candidate to get 50 per cent of votes. If no one wins in the first round, the candidate with the fewest votes is knocked out, and the second preferences of people who voted for them are redistributed to other contenders. This continues round by round until one candidate receives 50 per cent of votes.

Supporters say MPs have to work harder because they need to seek the backing of 50 per cent of voters, it gives you more choice in who becomes your MP and will cut the number of safe seats where MPs get a “job for life”.

But critics say some people will have their vote counted more than once, it is complicated, it will lead to more hung parliaments because the Liberal Democrats would be expected to get more seats, and it would be expensive to introduce and is only used by three countries in the world.