The party system in the People's Republic of China (PRC) is significantly different from those of Mexico, Japan, and the United Kingdom. The PRC is a socialist republic, meaning a single vanguard party (in this case, the Communist Party of China [CPC]), has a special role in the affairs of state. As is customary in socialist states, minor parties exist, however, these are corralled into a national front (termed the "United Front" in the PRC) in which the CPC has a statutorily guaranteed, leading role.
The CPC, in many respects, functions as a state itself. For instance, the PRC maintains no military forces of any kind. Rather, the CPC maintains military forces in the form of the People's Liberation Army (PLA) and the People's Liberation Army-Navy (PLAN). which fill the role that national armies do in other states.
Elections to the lower-level legislative bodies, which ultimately elect the Supreme People's Assembly, are dominated by CPC candidates. Though there is no legal requirement that candidates be CPC members, the structural advantages afforded the CPC all but guarantee CPC super-majorities.
By contrast, the party system in Mexico, Japan, and the United Kingdom is of a pluralist nature, meaning parties are all legal equals to each other. In other words, for instance, the British Labour Party has no more rights and privileges than the British Conservative Party.
The differences between the orientation of parties in China and in Mexico, Japan, and the United Kingdom are borne out of the revolutionary character of the Chinese state, versus the constitutional construction of Mexico, Japan, and the United Kingdom, which were influenced by parliamentary experiences common in western Europe.