Once the votes have been cast, the AV count is pretty similar to FPTP, but with multiple rounds.
It’s quite similar to reality TV shows, like X Factor or Strictly Come Dancing: whoever is least popular in each round is eliminated. The difference is that there’s a week between rounds on TV, so you can change your preference; that would cost hundreds of millions of pounds for general elections, so the rounds happen immediately with no change in preferences.
Here’s an example:
- Candidate A: 67%
- Candidate B: 19%
- Candidate C: 14%
Candidate A has already secured a true majority in this election, so they are elected, and the count is finished, just like FPTP.
Another (more realistic) example, based on the 2010 general election:
- Conservatives: 36%
- Labour: 29%
- Liberal Democrats: 23%
- Others: 12%
Assume for this that the “other” candidates are one party. They are least popular, and so are eliminated. Their votes are transferred to voters next alternative preferences, and counting goes on to round 2.
At each round, the least popular candidate is eliminated until there are just two candidates left. One of these must get more than 50% of the vote, unless there is a tie, so becomes elected, with broad support from the voters.