One of the most striking features of the political system in the more than four decades since independence has been the existence of viable and generally stable political parties. In the general elections held between 1952 and 1977, a two-party system emerged in which the UNP and the SLFP alternately secured majorities and formed governments. Observers noted, however, that one major failure of the two-party system was the unwillingness or inability of the UNP and the SLFP to recruit substantial support among Tamils. As a result, this minority was largely excluded from party politics.

On the basis of ethnicity, three types of parties could be defined in the late 1980s: Sinhalese-backed parties including the UNP, the SLFP, Marxist parties, such as the Lanka Sama Samaja Party (LSSP) and the Communist Party of Sri Lanka, and the numerically insignificant splinter groups a largely inoperative Tamil party system composed of the Tamil United Liberation Front (TULF) and other minority-oriented parties, such as the Ceylon Workers' Party, which enjoyed the support of the Indian Tamils, and the Sri Lanka Muslim Congress. The situation was complicated by the fact that extremist groups, such as the Sinhalese-based People's Liberation Front (Janatha Vimukthi Peramuna--JVP) in southern Sri Lanka and the Tamil Tigers based in the Northern and Eastern provinces, challenged the legal parties for popular support. By the late 1980s, both the intransigence of the Jayewardene government and the use of intimidation tactics by extremists in Jaffna District and parts of Eastern Province dramatically reduced popular backing among Tamils for the relatively moderate TULF.

The political party system was also weakened by the determination of the UNP leadership to retain a solid parliamentary majority through the use of constitutional amendments (see Government Institutions , this ch.). During the 1980s, various UNP measures undermined the balance between the two major parties that had been an important factor behind the political stability of the years between 1952 and 1977. The extension of the life of Parliament until 1989 and the passage of the amendment prohibiting the advocacy of separatism, which resulted in the expulsion of TULF members from Parliament, created new political grievances. The Jayewardene government's decision to deprive SLFP leader Sirimavo Bandaranaike of her civil rights for seven years for alleged abuses of power in October 1980 also weakened the two-party system because it deprived the SLFP of its popular leader.

Despite drastic constitutional changes since 1972, the party system's British heritage is readily apparent in the clear distinction made between government and opposition legislators in Parliament (sitting, as in Westminster, on opposite benches) and provisions in the 1978 Constitution to prevent defections from one party to another, previously a common practice. Backbenchers are expected to follow the initiatives of party leaders and can be punished with expulsion from the party for failin14d ing to observe party discipline.

Data as of October 1988