Not quite. The Prime Minister is the MP who can command a majority in the House of Commons.
An important distinction since there are more than two parties with MP’s. 
Right. Given party discipline, that is likely to be the leader of the party with a majority in the Commons. There are two cases where they aren’t the same:
(1) If no party has a majority, then the parties and their leaders will try to get together a coalition with a majority. Such a coalition might include independent members. (Independents have been crucial members of governing coalitions in some Australian state parliaments).
(2) If a party splits, so that some members of the ruling party no longer support the government on crucial issues. An example of this came in the Australian Parliament in 1941, when a small (but crucial) number of members of the governing United Australia Party voted for an amendment to a supply bill*. This led to the Deputy Prime Minister being appointed as Prime Minister, follwed by an election in which the opposition party won.
- The amendment was to change an item in the bill by one pound – a purely symbolic gesture, simply intended to test support for the government. I’ve read some of the Hansard for the debate: it’s quite amusing, as members get up and say that they aren’t interested in this one pound – they just want to pass a motion of no confidence in the government.
Actually the Prime Minister is whoever the Queen says it is. By convention it is the the leader of the majority party in the House of Commons. Whether she would actually appoint someone else and what would happen is another point.
The Queen also nominally calls elections and has the power to summon and dissolve parliament. By the Parliament act of 1911, parliament must meet at least once a year
and elections for a new parliament at least once every five years. By convention she is obliged to follow the recommendations of the Prime Minister - provided the Prime Minister has a majority in the House of Commons.
Yes, I know. 
His predecessor in the job, one Archibald Philip Primrose (aka the 5th Earl of Rosebery), holds an unusual, and some would say trivial, record. As far as I’m aware no other sitting British Prime Minister has owned an Epsom Derby winner, whereas he had two (Ladas in 1894 and Sir Visto in 1895) despite holding office for just over 15 months.
I have no excuse for offering this remarkable piece of information other than a genetic prediliction for wandering off-topic.
Conventions can be at least as strong as black-letter law in UK constitutional issues. One basic convention is that the PM must be able to get supply and taxation bills passed in the Commons, since otherwise HM’s government simply cannot carry on. There can be circumstances where the Queen has to make a judgment call on the matter (e.g., when no party or coalition has a majority, or in the past when the Conservative Party did not elect leaders), but if an MP clearly controls majority vote in the Commons, the Queen has no choice. If she were to ignore this, it would be at her peril: it could quite easily mean the end of the monarchy.
I don’t know how true this is in British politics, as Canadian practice has diverged in many ways over the years, but it’s not even necessary for the Canadian PM to be an MP. Mackenzie King was defeated as an MP candidate in both the 1925 and 1945 Canadian general elections in which his party won the overall majority. In both cases he was PM when the election was called, and remained PM afterwards as leader of the majority party (although he was quickly elected to the House through hastily called byelections in “safe” Liberal ridings vacated by by the resignation of a loyal MP).
Although Canada actually has a formal written Constitution, it barely mentions the office of Prime Minister at all (and then only in determining the makeup of any constitutional conventions for future amendments). Like the UK, the actual day-to-day functioning of the Canadian Parliament is heavily dependant on unwritten conventions and historical precedent.
Under the Australian Constitution, a minister must become a member of the Federal Parliament within 30 days. There have been two times when a PM was not an MP:
(1) The first PM, Edmund Barton, was appointed as PM before the first federal election, and so before there were any MPs.
(2) In 1968, following the disappearance of Harold Holt, Senator John Gorton was appointed as PM. Although it is legal for a senator to be PM, it was decided that it’s against convention, and Gorton resigned from the Senate and contested Holt’s vacant seat in the House of Representatives, so that for about 3 weeks he was a member of neither house.
Australia has similar unwritten conventions, even though it has a written Constitution, and neither the Prime Minister nor the Cabinet are mentioned in the Constitution.
The cabinet it, isn’t it? just under the formal name of “Federal Executive Council”?
No, the Cabinet is the real decision-making body, while the Federal Executive Council is a pure formality, which only puts a rubber stamp on decisions already made by Cabinet or by individual ministers.
Just how rubber-stampish it is is shown by the fact that the Governor-General, who is supposedly being advised by the Federal Executive Council, is not even required to be present at its meetings:
So if neither the Cabinet nor the Prime Minister are mentioned in the Constitution, how is there a constitutional requirement that a minister must become a member of the federal Parliament within 30 days? 
Because the Prime Minister is also a “minister of state” and ministers are mentioned in the constitution.
so all Cabinet ministers are members of the Federal Executive Council, but not all members of the Federal Executive Council are members of the Cabinet?
Just wanted to say, Jeffrey Archer’s First Among Equals is an excellent novel about British politics, following three MPs in their careers from the late 1960s to the early 1990s (Archer, a former MP and now a peer, wrote it in 1984, IIRC) as each vies to become Prime Minister. A great read for anyone interested in goings-on at the Palace of Westminster.
Yes. Under section 64 of the Constitution all ministers (whether in the Cabinet or not) are members of the Federal Executive Council.
That’s correct. The Cabinet is the **inner core ** of the ministry and is made up of the more senior ministers only. This link gives details of those ministers who are in the Cabinet and those who are part of the “Outer Ministry”.
I’m still a bit puzzled. If the Executive Council is composed of the Prime Minister, the Cabinet, and the junior ministers, that collectively is the most powerful group of politicians in the federal government. Why do you refer to them as a “rubber-stamp”?
They may all be members of the Federal Executive Council, but they don’t go to its meetings:
The process is:
- Cabinet actually makes the decisions;
- these decisions are then ratified by a meeting of the Federal Executive Council to preserve the Constitutional requirements under sections 61 and 62 that the executive power of the Commonwealth is exercised by the Governor-General, as advised by the Federal Executive Council;
- but the actual meetings of the Federal Executive Council don’t even require the presence of the Governor-General - merely a small number of ministers “officially ratifying” the decisions that the Cabinet has already made. It’s in this sense that the Federal Executive Council is simply a “rubber stamp”, since it’s practicaly unthinkable that it would refuse to ratify a Cabinet decision.
It says in Salisbury cathedral where a copy of the Magna Carta is displayed that much of the U.S. constitution is based on it.
Nothing in the Constitution itself appears in Magna Carta. MC was a statement of certain rights of the Church and the nobility; as such, it prefigures certain ideas that appear in the Bill of Rights, most notably the 6th Amendment.