Your guide to the different voting systems on 6 May

British elections are held using at least four different electoral systems, as John Rentoul explains

Nicola Sturgeon’s feud with Alex Salmond has drawn attention to the different electoral systems in the UK (AFP/Getty)

The eruption of the feud between Alex Salmond and Nicola Sturgeon has drawn attention to the system of semi-proportional representation used in the Scottish parliament elections. Salmond’s new party, Alba, has been launched to take advantage of the list system used to “top up” party representation.

Which is a reminder that there are several different electoral systems across Britain that will be used on 6 May. Here is a rundown of what kind of ballot papers voters can expect in different parts of the country.

Welsh parliament

Wales uses an added-member system like the Scottish parliament, with each elector having two votes, one for a constituency MS (Member of the Senedd) and one for a party’s regional list. There are 40 constituency MSs and 20 regional list MSs. Each vote is marked with a single X. Constituency MSs are elected by first past the post (whoever obtains the most votes wins), while regional MSs are elected in such a way as to make the result in each region as proportional to the second (party) votes as possible. Last time, for example, Labour won all seven of the constituency seats in South Wales West, so Plaid Cymru, the Conservatives and Ukip were entitled to four seats between them from their top-up lists.

London mayor and assembly

The London assembly is elected using the same added-member system, with each elector having two votes: one for each of 14 large constituencies, and one for 11 additional members elected from London-wide party lists. Voters will also have a third ballot paper for the election of the mayor. This election is by the supplementary vote system, by which voters mark their first and second preferences, each with an X in a different column. If no candidate wins 50 per cent of first preference votes, all candidates apart from the top two are eliminated and their second-preference votes are allocated between the top two.

Directly elected mayors

The mayors of metropolitan areas or cities are also elected by the supplementary vote system, which Priti Patel, the home secretary, announced this month that the government wants to abolish. She said the government intended, after this year’s elections, to change supplementary vote elections to first past the post – “in line with the government’s manifesto position in favour of first past the post, which provides for strong and clear local accountability, and reflects that transferable voting systems were rejected by the British people in the 2011 nationwide referendum”.

Police and crime commissioners

Police and crime commissioners are being elected across England and Wales (outside London), also by the supplementary vote system. The government’s decision to change the system is surprising, because the most notable occasion on which the supplementary vote produced a different result from first past the post was when John Prescott, the former deputy prime minister, stood to be police and crime commissioner for Humberside in 2012. He won the most first-preference votes, but was defeated by Matthew Grove, the Conservative, after the transfer of second preferences.

Local councils (and the Hartlepool by-election)

The only votes on 6 May to use the pure first-past-the-post system are those for local councils, and for the Hartlepool by-election. In most places, this means marking the ballot paper with a single X, and the candidate with the most votes being elected even if they do not have a majority of votes cast. In some cases the whole council is up for election, in which case voters in multi-member wards will mark the ballot paper with as many Xs as there are councillors representing that ward, but in most areas only one seat is up for election each year. In multi-member wards, the top three candidates are elected (or however many seats there are to be filled).

Single transferable vote (STV)

Finally, there are a few local council by-elections in Scotland and Northern Ireland, which will use the single transferable vote system, by which voters mark a single ballot paper with numbers to show their first, second and subsequent preferences.