Strong prime ministers in these so-called Westminster systems are often endowed with considerable constitutional powers, including the power to change the structure of ministries (and, hence, the number of powers of their cabinet colleagues) as an executive action without seeking new legislation. They can also dissolve the legislature and call for new elections at any point during their term (though these powers are exercised by the British prime minister only by convention); this power is quite useful, enabling a prime minister to hold an election at politically advantageous times.
New prime ministers typically are strongest immediately following an election; their power and prestige may decay if the government becomes unpopular. Because Britain and most Commonwealth countries have adopted plurality-based national electoral systems, coalition governments are rare in Westminster systems, and when they do occur (as in India, for example, in the 1990s and early 21st century) the prime minister’s political predominance is considerably reduced (see plurality system).
