I'm still not entirely certain on what it is you are asking, but I'm going to attempt to answer as best I can.
The Australian Constitution deals with the provision of government primarily at a Federal level (although it does deal in some parts with States - who have their own Constitutions - and the caveat that any inconsistencies between the two are dealt with by the Australian Constitution taking precedence).
Part of it spells out exactly how government in Australia is to be formed:
- Legislative power
The legislative power of the Commonwealth shall be vested in a Federal
Parliament, which shall consist of the Queen, a Senate, and a House of
Representatives, and which is hereinafter called The Parliament, or
The Parliament of the Commonwealth.
It also explicitly describes how, and in what number, representatives are elected. For the Senate:
The Senate shall be composed of senators for each State, directly
chosen by the people of the State, voting, until the Parliament
otherwise provides, as one electorate...
...Until the Parliament otherwise provides there shall be six senators
for each Original State. The Parliament may make laws increasing or
diminishing the number of senators for each State,5 but so that equal
representation of the several Original States shall be maintained and
that no Original State shall have less than six senators.
The senators shall be chosen for a term of six years, and the names of
the senators chosen for each State shall be certified by the Governor
to the Governor-General.
This was amended to 12 senators for each State under the Representation Act 1983, s. 3
For the House of Representatives:
The House of Representatives shall be composed of members directly
chosen by the people of the Commonwealth, and the number of such
members shall be, as nearly as practicable, twice the number of the
senators.
The number of members chosen in the several States shall be in
proportion to the respective numbers of their people, and shall, until
the Parliament otherwise provides, be determined, whenever necessary,
in the following manner: (i) a quota shall be ascertained by dividing
the number of the people of the Commonwealth, as shown by the latest
statistics of the Commonwealth, by twice the number of the senators;
(ii) the number of members to be chosen in each State shall be
determined by dividing the number of the people of the State, as shown
by the latest statistics of the Commonwealth, by the quota; and if on
such division there is a remainder greater than one-half of the quota,
one more member shall be chosen in the State.
But notwithstanding anything in this section, five members at least
shall be chosen in each Original State.
However, unlike the Senate, Parliament has the ability to adjust the numbers in the House of Representatives without altering the Constitution:
- Alteration of number of members
Subject to this Constitution, the Parliament may make laws for
increasing or diminishing the number of the members of the House of
Representatives.
So the current numbers stand at 76 Senate seats and 150 in the House of Representatives.
As for your question:
Constitutionally speaking is there anything stopping the federal government ditching both houses and creating a one seat parliament and then running an election every 3 to 4 years. I'm interested in the constitutional position rather then the likelihood of this.
The Constitution itself establishes the structure of Parliament, and dictates what powers, terms and form it takes. So any change to the structure of Parliament would first have to involve a rather significant change to the Constitution itself - which would first have to be ratified by a Referendum. Interestingly enough, Australia has had a total of 19 referendums since 1901, with only 8 changes (out of 44 proposed) accepted.
