Tuesday, April 6, 1999 Published at 21:33 GMT 22:33 UK
Why change the system?
The 1997 General Election: vote share compared to share of the seats
The Additional Member System is a form of proportional representation and was brought in by the government to try to balance some of the effects of a purely First Past The Post system.
Under First Past The Post, the candidate with the highest number of votes is elected even if he or she gets the support of less than half the electorate. This means that parties frequently win lots of seats despite not having a majority of the popular vote.
In the 1997 UK General Election, for example, Labour won 64% of the MPs with only 45% of the vote. In Wales, the Conservatives won no seats at all, despite electoral support of 19.6%.
Supporters of FPTP argue that it encourages clear results and maintains a strong link between voters and their representatives.
However, backers of proportional systems believe they result in governments which represent the views of the electorate more closely.
Since taking power, the Labour Government has explored various options and these elections are the first time that a proportional system is being used for elections in England, Scotland or Wales.
Other proportional systems will be used for the European elections in June and for the election of London's mayor next year and it is possble that future general elections could have some form of proportional representation.
The changes are not universally popular within the Labour Party, not least because one consequence is that its electoral rivals seem likely to do better under the new systems than they did in 1997.