Science battles Government over cannabis

We have a bicamaral legislative.
The House of Lords which used to be hereditary but is now mostly appointed. They ratify legislation and can hold up or ask for rewrites for legislation they don't like. Ultimately the House of Commons can force legislation through an unwilling House of Lords but it takes a lot of effort and unity. Peers(Lords/Baronesses etc) are appointed by the Prime Minister but are generally not political appointments. People are appointed to it because of respect for their expertise, knowledge or judgement. For example most ex Prime Ministers are now peers. The House of Lords is a pretty independent body because the Government has no power over them.

The House of Commons is the legislative. It is made up of Members of Parliament (MPs) who are each elected from a local constituency whom they serve. They are generally part of our three main political parties but anyone can (and often does) stand in elections for Parliament. Elections are held on a first past the post basis for constituencys so the winning party only needs a plurality of the vote rather than a majority. In fact, a majority of the vote is pretty much unheard of but the system generally gives the winning party a majority of MPs. The House of Commons holds the power in British politics and can make and unmake laws pretty much at whim with a majority. There is no constitution, a Parliament is not bound by any previous Parliament and cannot bind any future Parliament. Its powers are limitless.

The House of Commons can invite any member of it to form a Government. In practice the leader of the party with the majority of the house becomes PM and forms a Government. Usually he draws the cabinet from his own MPs but they can also come from the House of Lords (Blair appointed one of his old roommates to the house of Lords then brought him into his Government). The Government then drafts legislation to be presented to the House of Commons where it is passed by a simple majority. From there it goes to the House of Lords where it can be amended, rejected or passed. The Government has a lot of power over the MPs because they generally get their job by the virtue of the party they stand for. There have been cases of MPs getting fired for refusing to follow the party line and being re-elected by their constituency but these are extremely rare, generally the Gov can bully MPs.

Until a month ago we had no Supreme Court. Without a constitution there is no real need for it. However there was a group within the House of Lords who were appointed to their peerage by virtue of their excellent legal knowledge, usually ex lawyers or judges. These were referred to as Lawlords and they had a special committee within the House of Lords. However they are now referred as the Supreme Court, no longer get to vote in the House of Lords, and function mainly as an advisory body.

Because our political system is organic and evolved rather than being designed there are no real checks and balances nor separation of power. The Gov must be part of the legislative, the judiciary until recently was part of the upper body of the legislative. It mostly works the way it does because of tradition but theoretically if half the MPs tomorrow decided to invite a random hereditary Lord to form a Gov then Brown (our PM) would be deposed and that Lord would be the new PM. The Gov used to just be unofficial people with sufficient support among MPs to get legislation passed and evolved into a position appointed by a majority of MPs. Twelve years ago the Conservative Gov of John Major actually had less than half the MPs in the House of Commons due to defections and couldn't really pass any legislation. However the opposition party, Labour, had insufficient votes to challenge him and form their own Gov.

The PM has been unofficially devolved many of the powers of the monarch. He can appoint peerages, declare law in his own right, call elections, fire and appoint his cabinet and declare war/peace. He has far more powers than any constitutional system would dare give a President. Indeed during the Second World War Winston Churchill was not elected PM by the people but led a coalition of MPs in revolt against Chamberlain (previous PM) after the fall of France and was invited to form a Gov. Once in power he decided to indefinitely suspend elections to Parliament. Hitler had a harder time becoming a dictator than Churchill did. However once the war had decisively turned in the favour of the allies he called an election which he lost to Clement Attlee. Our system gives a great degree of flexibility because it is based on tradition rather than constitution. Similarly it updates itself to stay relevant to the context in which it exists. For example, a PM declaring war by his own power would be frowned upon now as undemocratic. When Tony Blair invaded Iraq he invited the House of Commons to have a debate on the matter and then they declared war on Iraq. Although the PM still retains the power to declare war it is likely that Blair set a tradition whereby war is declared by the House of Commons in future.