The Financial Review Style Book
Capitals for Prime Minister and Premier (with or without a name). Minister is capped when part of a title (i.e. with portfolio, or portfolio and name) but is lower case otherwise. Senator is capped as part of a name but otherwise is lower case.
Ministry and shadow ministry are capped as part of a name (the Federal Ministry, the second Keating Ministry, the NSW Shadow Ministry) but are lower case otherwise.
Capitals for the Leader of the ----- Opposition. In the first instance use the form "the Leader of the Federal Opposition, Mr Joseph Doe" or "the Leader of the NSW Opposition, Mr Marcus Doe". In later references simply say "the Opposition Leader" or, if it is necessary to distinguish between two Opposition leaders, "the NSW Opposition Leader". Do not abbreviate West Australian and South Australian in this context.
Use lower case in general references to an Opposition spokesperson. Note that our style is to avoid the use of the term "shadow". Exceptions are: the Shadow Cabinet, the Shadow Ministry, the Shadow Attorney-General and the Shadow Treasurer. Thus, our style is: the Federal Opposition's spokesman for health, Dr Robert Doe.
Capitals for Cabinet, Caucus, the Speaker, Leader of the House, Leader of the Government in the Senate, Chairman of Committees, Question Time. Use lower case for a group with only a general description (a committee of Cabinet) but upper case when giving the formal name of a parliamentary committee in full.
Capitals for parliamentary leaders of political parties (e.g. the Leader of the National Party, Mr Tom Doe) but lower case for non-parliamentary office holders such as national, federal and State presidents (e.g. the national president of the Australian Labor Party).
Plurals are also lower case: prime ministers, premiers, governors-general and so on. (The exception is Speakers.)
Short forms of legislatures take capitals: the House, the Assembly, the Council (Legislative Council), the Commons, the Lords.
The Australian Labor Party (and the Labor Party), the Liberal Party, the National Party; thereafter the party, and similarly for all political parties in Australia or overseas.
Government, meaning "Executive", is capped when preceded by the definite article "the" ("the role of the Federal Government") and when referring to specific past or present administrations (the Federal Government, the NSW Government, the State Government, the Whitlam Government, the Government of Mr Malcolm Fraser). Adjectivally, it should be capped only in the context of a plan, policy or action of a specific government (a NSW Government plan, a Keating Government policy - but NSW government buses, Victorian government schools). With the exception of the examples just mentioned, "government" is lower case when preceded by the indefinite article "a" ("a government committed to social change"). It is also lower case in the plural (State governments, the role of federal governments); when referring to a hypothetical future government; and in a general sense, as in "the art of government". If in doubt, the general rule is upper case when defining and singular (but not hypothetical) and lower case otherwise.
The Opposition takes a capital, as does Address-in-Reply.
Frontbench, backbench as adjectives and nouns for the people sitting there, but the front bench and the back bench for the places where they sit. Frontbencher, backbencher.
The Left, the Right, Centre Left, Centre Unity; otherwise lower case for groupings within parties: the left wing, right-wing tendencies, left of centre.
In the US, congressmen are members of the House of Representatives, not the Senate.