Here are three differnet types of voting systems used within the United Kingdom
First Past the Post (FPTP)
This system is used during general elections and some other ballots in the UK. Each voter can cast one local vote, and the candidate with the most votes becomes the MP or Councillor. It has historically usually produced single-party governments.
Single Transferable Vote (STV)
Used for local and devolved elections in Northern Ireland. In each area, a certain number of seats are available, and voters choose a range of candidates in order of preference. Seats are allocated as soon as a candidate reaches a ‘quota’ (specific number) of the votes, and votes can be reallocated to reduce ‘wasted’ votes.
Additional Member System (AMS)
Voters in elections for the Scottish Parliament and the Welsh Assembly have two votes – one to elect a member for their local constituency and one to indicate their choice of party. This is a hybrid system: the constituency votes are counted using the FPTP system, and the second is used to select regional members proportionally. It can make coalitions more likely.