The Westminster system is the name of the way legislatures operate in a number of countries, all of which at one time or another were part of the British Empire. Its birthplace is Great Britain, but it is now used in India, Australia, Canada, as well as Jamaica, Singapore, South Africa and Malaysia. These countries have bicameral legislatures, meaning they have a lower house (in which the Prime Minister must be able to hold a majority) and an upper house. The composition of the two houses varies between countries, but they all make laws in remarkably similar ways.
There are generally two legislative assemblies under the Westminster System, an Upper and a Lower House. In Britain these are known as the House of Lords and the House of Commons respectively. Bills (proposed laws, as distinct to acts which are actual statutes) can be proposed in either house. The vast majority of them are introduced by members of the Cabinet (who are themselves elected representatives who sit in the legislature, as opposed to the American Cabinet, who are approved by the Senate but banned from sitting in Congress), but some time is also devoted to bills introduced by private members. This time is limited because in the nineteenth century it was common to block effective government action with endless streams of private member's bills that ate into Parliament's time.
The bill is first read in the house it was introduced into. In Britain the government introduces only the most uncontroversial bills into the Upper House, wanting their proposals to gain the support of the elected representatives in the Lower House. As its own supporters are dominant here, this is the safest bet to get it past the first vote. The first reading of the bill is a mere formality, and is the occasion of the publication of the government's explanation of and case for the bill. This material will tend to be labelled "spin" by some section of the media, but it is the job of the Members of Parliament to consider the problem the bill is designed to solve and how effective a job it does.
Their first opportunity to speak their mind comes at the second reading of the bill, where a vote on its general principles is taken after a debate. If the government is beaten on this vote then it is considered a major setback. In the Lower House, such a defeat would represent a failure to carry its own party (or in rare cases coalition parties) with it. To avoid such an embarrassment where it is considered likely, whips may be used. No, sadly no-one is going to actually bludgeon George Galloway - a "whip" is an order from the government that members of the party are expected to act a certain way when voting on a particular bill. "One line" whips indicate they may vote as they wish, whereas "two line" whips allow them to absent themselves if they cannot bring themselves to vote positively. The dreaded "three line" whip compels them to vote positively, although a large scale revolt would make the government rethink.
If the bill passes this stage, it's ready for committee. Committees are comprised of a small number of members of the house. In the Commons, they tend to be between a dozen and fifteen people. These people will tend to have specialized knowledge of the technical details of legislation in the area under consideration, and the party allegiance of members will be a microcosm of the party composition of the house as a whole. On important matters such as the annual budget, the whole house will sit 'in committee'. This is also the usual practice in the Lords on all matters, and in Australia, where committees are rarely used.
At the committee stage the government can strengthen its bill, and make concessions based on the outcome of earlier debate. The government's priority is to make sure the bill emerges from committee in a form that will be ultimately passed by the house, whereas the opposition may seek to emasculate the bill or amend it radically. It may undergo large-scale change at this stage, and when it emerges its amendments are considered by the entire house. Then the third reading occurs, at which point a final debate and vote occurs on the bill. In the Lords it may be amended further at this stage, whereas in the Commons no further amendment is permitted.
The bill is now sent to the other house. The Commons has the power to tell the Lords to stuff it, but things aren't so simple for the latter. They can reject most bills from the Commons initially, but their powers to stall for ever are limited in Great Britain by the Parliament Acts. The first of these was passed in 1911, which provides for the Commons to force a bill by passing it in three subsequent sessions. So-called "money bills" which were designated as such by the Speaker of the Commons could be passed in a mere month. These bills deal with taxation, historically the perogative of the Commons after the great constitutional battles fought centuries earlier between monarchy and Parliament.
The second Parliament Act, passed in 1949, allowed the Commons to force a bill in a mere year. It was most recently used to ban fox hunting. The Parliament Acts have rarely been used as the Lords has been tamed over the years, but the threat of it has probably made a significant impact on this supineness. It is also against the so-called Salisbury Convention for the Lords to reject a bill that was promised as part of an election manifesto. This convention dates from the time of the second Parliament Act, which had been introduced by Labour Prime Minister Clement Atlee. Lord Salisbury, the Conservative leader of the House of Lords, did not think the Lords should stand in the way of the clear mandate for nationalization that the Commons had received from the electorate. Declining voter turn-out has made this a touchy subject in recent years.
The house to which the bill is passed can propose amendments to the bill and put it through committees, then pass it back. The Salisbury Convention does not prevent the Lords from proposing amendments so long as they are not against the spirit of the bill. The bill may now pass between the two houses several times as amendments are proposed and rejected. In Canada, the Upper House (Senate) has the ability to destroy a bill by refusing to agree with it. In Australia, the Governor-General may eventually dissolve Parliament and then force the bill if the newly-elected lower house again votes in favour. In Britain, the Parliament Acts may be invoked if agreement is not reached. If such drastic measures are not considered worthwhile, the bill is lost.
Once both houses are agreed on a final version of the bill, it becomes law. The final step is for the bill to gain the Royal Assent, or the assent of the Governor-General in the case of Commonwealth states. The monarch or their representative Governor-Generals almost always act only in accordance with constitutional convention and the advice of the Prime Minister. Nowadays this step is almost entirely ceremonial, although it is a necessity before a bill becomes a law. Cermonies of the granting of assent are often elaborate in Westminster, but tend to consist of a simple signing in the Commonwealth nations.
Such a rigorous and time-consuming process is necessary given the all-consuming sovereignty of Parliament in most nations that practice the Westminster system. In Britain, Parliament's power is so absolute that it could legislate "Noung is to be shot at dawn" if it wished; only precedent, my low profile and probable (okay, possible) public outrage prevent it from doing so. Such far-reaching power must be exercised wisely, and its diffusion between hundreds of people ensures it is hard for such power to be exercised dictatorially. Only about fifty acts get passed each year in Britain.