Not least the big electoral success of the Social Democrat and the Liberal Party alliance in the 1983 general election, in which their share of the vote was only 2.2 percent behind that gained by the Labour Party, has led to questions being raised as to whether Britain really does have a two-party system. Admittedly, this large share of the vote was hardly translated into seats in Parliament. Capturing 25.4 percent of the vote, the alliance held only 23 seats in parliament. In contrast, the Labour Party was able to send 209 MPs to London with 27.6 percent of the vote. At a regional level, however, there are clear indications of a firmly founded three-party system, and in Wales and Scotland even of a four-party system. And what is more, those holding the British two-party system as a myth were able to draw on historical facts and not just the current situation (...).

Despite these indisputable changes, the British party system can still be regarded as a two-party system at its core. Evidence for this includes the way in which the system functions. Indeed, this system is also considered by the political elite as enjoying additional protection from the first-past-the-post system, which ensures dualism between the ruling party and opposition party. Evidence is also provided by Britain's political culture, which, especially among the next generation, supports and carries the first-past-the-post system and the principle of one-party rule despite the fact that the system's unfairness is known and, asked in an abstract way, that the majority of people support a more fair electoral system. Yet given the alternative between electoral fairness and effective government, a large majority of people would like to see the present system maintained, especially supporters of the Conservatives followed by those of the Labour Party and the Scottish National Party.

It has often been claimed that the days of the two-party system in Great Britain are numbered and the party duopoly is only being maintained with the help of the first-past-the-post system. Supporters of this theory take the following indicators as proof of a two-party system:
1. On average there are less than three (serious) candidates per constituency.
2. The party duopoly regularly achieves more than 90 percent of the votes cast.
3. One party has a sufficient majority in Parliament.
4. Slight swings in voting patterns can bring about a change in government.

If we take these conditions and apply them to the situation in Great Britain, it would be fair to speak of something other than a two-party system. According to Sartori, on the other hand, a party can only be regarded as being a relevant part of the party system when it has seats in parliament and when it has coalition or government potential or disruptive potential, this means, when it participates in a positive or negative way in the formation of government. According to these relevance criteria, then, Great Britain can still be regarded as having a two-party system. Indeed, the way in which it functions also supports this claim. "Classifying party systems according to numerical criteria means classifying them on the basis of their format, that is, how many parties are contained within them. Yet this format is only relevant insofar as it influences the mechanics, that is, how the system works." In stark contrast to the instability of government majorities during the 70s, the 80s are characterized by a clear consolidation of these system-based mechanics.

The ability of the two-party system to function is founded on three pillars:
1. At an institutional level on the democratically-founded dualism between the government and the opposition, which is expressed in the first-past-the-post system among others.
2. At a socio-structural level on the social and regional ties of voters to the party duopoly.
3. At a habitual level on the political culture, which regards the presence of effective government with clear policies as being more important than a better reflection of true public opinion in Parliament. This tendency to rate the principle of participation below that of legitimate and effective government is characteristic of British political culture.

Indeed, the roots of this two-party system go deeper than the advocates of this end-of-duopoly theory would have us believe. The large parties have a great deal of time available to them to adjust themselves to new voting patterns and changes in the party marketplace long before other parties might become dangerous. These other parties perform a complementary function. They are used to signal dissatisfaction and protest, and sometimes even total mistrust in the competence of the large parties.