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Although First Past the Post is used to elect MPs to the House of Commons, it is far from the only electoral system in use within the United Kingdom. Since devolution in 1999, more proportional and hybrid systems have been used to elect the devolved legislatures and several other bodies. This lesson examines those systems — the Additional Member System (AMS), the Single Transferable Vote (STV) and the Regional List — explaining how each works, the effects each produces, and the advantages and disadvantages of each. Mastery of these systems is essential for Component 1 (Paper 1), because the existence of different systems within the same country allows you to compare their real-world consequences and to build evidence-based arguments about electoral reform.
Proportional representation (PR) refers to any system in which the share of seats a party wins is broadly proportional to the share of votes it receives. PR systems are designed to remedy the central criticism of FPTP — its disproportionality — by ensuring that seat shares track vote shares far more closely. The UK uses several such systems for elections below the level of the Westminster Parliament:
| System | Where Used | Type |
|---|---|---|
| Additional Member System (AMS) | Scottish Parliament, Welsh Senedd, London Assembly | Hybrid (mixed) |
| Single Transferable Vote (STV) | Northern Ireland Assembly, Scottish local elections | Proportional |
| Regional List | Formerly UK European Parliament elections | Proportional |
This patchwork of systems is sometimes described as making the UK a natural laboratory for studying electoral systems. The same voters, in the same country, behave differently and produce different governments depending on the system used. Understanding these systems is therefore essential both for comparing approaches to representation and for evaluating proposals to reform Westminster, because supporters of reform routinely point to the devolved bodies as proof that PR "works" in the British context, while opponents point to the same bodies to argue that PR produces unstable coalitions and weaker government. A key skill is to be able to deploy this evidence on both sides.
The reason these more proportional systems were adopted at all is itself instructive. When devolution was designed in the late 1990s, there was a deliberate decision not to replicate Westminster's FPTP for the new institutions. In Scotland and Wales the concern was partly that pure FPTP might allow a single party to dominate the new legislatures permanently, undermining the broad cross-party consent that devolution was meant to embody; AMS was chosen precisely to dilute that risk and to encourage power-sharing. In Northern Ireland the choice of STV was bound up with the peace process and the need for an electoral system that could fairly represent both communities and a plurality of parties within a power-sharing framework. The systems were thus selected with their effects in mind, which is why they are such useful evidence in debates about whether Westminster itself should change.
It is worth distinguishing carefully between three families of system, because confusing them is a common and costly error. Plurality systems (FPTP) elect whoever comes first, even on well under half the vote. Majoritarian systems (the Supplementary Vote and the Alternative Vote, covered in a later lesson) are designed to deliver a winner with majority support, but still elect single members and are not proportional. Proportional systems (AMS, STV, list) aim to make the overall composition of the chamber reflect vote shares. AMS is best described as a hybrid or mixed system because it grafts a proportional top-up onto an FPTP base. Keeping these categories straight is essential when answering comparative questions: a frequent and avoidable error is to describe the Supplementary Vote or the Alternative Vote as "proportional", when in fact they are majoritarian systems that elect single members and do not make the legislature reflect national vote shares at all.
AMS is a hybrid (or mixed) system that deliberately combines FPTP with a proportional list element, attempting to capture the benefits of both. It is sometimes called the Mixed-Member Proportional (MMP) system.
The Scottish Parliament is the standard worked example:
Because a substantial bloc of seats is allocated through the proportional top-up, the Scottish Parliament's composition is markedly more proportional than Westminster's, and single-party majorities are difficult to achieve. The system was in fact designed with this outcome in mind: those who established the Scottish Parliament wanted to avoid one party dominating, and AMS has duly produced a series of coalition and minority administrations. The Welsh Senedd and the London Assembly use the same basic AMS design, although the precise balance of constituency to list seats differs between the bodies.
It is worth understanding why the top-up corrects disproportionality. Imagine a party that wins a large share of the regional vote but, because its support is spread evenly, wins few or no constituency seats. Under FPTP that party would be heavily under-represented. Under AMS, the allocation formula recognises that the party's overall seat share lags behind its vote share and awards it list seats to close the gap. Conversely, a party that has "over-performed" in the constituencies — winning more constituency seats than its regional vote share alone would justify — receives few or no list seats, because it has already secured its fair share. The list seats therefore act as a corrective ledger, topping up the under-represented and withholding from the over-represented until the chamber as a whole roughly matches the regional vote. This is the essential difference between AMS and a parallel (non-corrective) mixed system, in which the list seats are simply added on top without reference to the constituency results and so do not correct disproportionality.
Because voters have two votes, they can engage in split-ticket voting — supporting one party with the constituency vote and another with the regional list vote. Some smaller parties have explicitly campaigned for voters' "second vote", arguing that a list vote for them is not wasted even where they cannot win the constituency. This has helped parties such as the Scottish Greens to secure list representation that FPTP alone would deny them, and it gives voters a more nuanced way of expressing their preferences than the single X of a Westminster ballot.
A distinctive feature of AMS is that it produces two types of member: constituency representatives elected by FPTP and regional (list) representatives elected from the party lists. This has generated genuine debate about whether the two types enjoy equal legitimacy. Constituency members can claim a direct personal mandate from a defined local electorate and a clear caseload of constituents; list members, by contrast, are elected to represent a much larger region and owe their place partly to their position on a party list. Critics argue this creates an awkward hierarchy and potential friction — for example, where a defeated constituency candidate re-enters the legislature via the list and then campaigns within the same area against the person who beat them. Defenders respond that list members perform a valuable role precisely because they are not tied to a single seat: they can take a regional view, take up causes that cross constituency boundaries, and ensure that areas dominated by one party still have representatives from a range of parties. Whether the "two classes" feature is a flaw or a strength is a matter of judgement, and a strong answer can use it to illustrate the trade-offs inherent in any hybrid design.
| Advantage | Explanation |
|---|---|
| More proportional | The corrective list element compensates for the distortions of the constituency results, producing a much closer fit between votes and seats than FPTP |
| Retains a constituency link | Voters still have a single, identifiable local constituency representative elected by FPTP |
| Greater voter choice | Two votes allow voters to split the ticket — for example, backing one party for the constituency and another for the list |
| Representation for smaller parties | Parties that struggle to win constituencies can still secure list seats, allowing parties such as the Scottish Greens to gain representation |
| Disadvantage | Explanation |
|---|---|
| Two classes of representative | Constituency MSPs and regional list MSPs may be perceived as having different mandates, roles and legitimacy, which can cause tension |
| Greater complexity | Having two votes counted in different ways is more complex for voters than a single X under FPTP |
| Coalition or minority government | AMS rarely produces single-party majorities, so coalitions or minority administrations are common, with the bargaining and potential instability that brings |
| Party control of lists | Party leaderships determine the order of candidates on the regional list, so voters cannot choose between individual list candidates |
STV is a fully proportional system that uses multi-member constituencies and a preferential (ranked) ballot. It is widely regarded as the system that maximises both proportionality and individual voter choice, and it is the system favoured by the Electoral Reform Society.
The genius of the transfer mechanism is that very few votes are wasted: a vote that cannot help its first-choice candidate — because that candidate is either already elected with a surplus or has been eliminated — flows instead to the voter's next choice. This is why STV consistently produces results that closely mirror the spread of voter preferences.
A simple worked illustration helps. Suppose a five-member constituency. Under the Droop formula, the quota is just over one-sixth of the valid votes — the smallest fraction such that no more than five candidates can reach it. A popular candidate who attracts, say, a quarter of all first preferences exceeds the quota comfortably and is elected on the first count; the votes they hold above the quota are then transferred to those voters' second preferences, so that none of that popular candidate's "extra" support is wasted. Meanwhile, candidates who attract very few first preferences are eliminated one by one, with their votes flowing to the next preference each voter has marked. Over successive counts, the five seats fill up with a mixture of candidates that reflects the balance of opinion in the constituency far more faithfully than five separate FPTP contests would. The price of this fidelity is complexity: the count takes far longer, and ordinary voters cannot easily follow exactly how the result was reached, which opponents argue weakens transparency.
In Northern Ireland in particular, STV is valued because it allows the proportional representation of the different communities and of a range of parties within each constituency, supporting the power-sharing settlement that underpins devolution there. By ensuring that no single bloc can monopolise representation in a constituency, STV helps to guarantee that minority traditions are heard, which is one reason it was considered appropriate for a divided society emerging from conflict. The use of STV for Scottish local elections, introduced in 2007, similarly broke the pattern of single-party dominance that FPTP had produced in many councils, ending the situation in which one party could control a council on a minority of the vote and forcing a broader sharing of local power. These domestic examples are valuable in essays because they show STV working in practice within the UK, not merely in the Republic of Ireland.
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