In British Politics, the Crown refers to the head of state; the monarch, as opposed to the jewelled crown worn by the Queen. The monarch has a very important political role to play in Britain, both constitutionally; regulating the country, and ceremonially. However, over the years the role of head of state has become less influential with more powers and responsibilities being granted to the elected Government. Despite this, the Queen still has an important role to play and is involved in many different areas of government affairs.
The monarchy is the oldest part of the system of government in the UK and so is very historically significant, as a result there are numerous traditions surrounding the Queen and the Royal family which are followed for the sake of tradition rather than because of their political influence. For instance, the members of the armed forces have to swear an oath of allegiance to the King or Queen because they hold the title of Head of the Armed Forces. As a result of this title, the monarch is the only person who is allowed to declare war on another country. However, the monarch does so on the advice of the Prime Minister and the Government and does not actually make the decision themselves.
So why is the monarch so important then? Well for starters, though the Government has more power than the Queen, without her the members of Government would not have their jobs in the first place. This is because, the day after a General Election, the Queen invites the leader of the winning party to become the next Prime Minister and form a Government, until they receive this invitation the winning leader is not yet Prime Minister and so has no power. The Queen also has to give her Royal assent, that is her approval, to government bills before they can be passed into law.
In addition to these powers, the Queen is also head of the Church of England and it is in her name that Justice is carried out in the courts of law. Therefore, the monarch has a very important role to play in British Politics, even if this role is mainly ceremonial. Yet, even though their power has diminished, the British monarch has the advantage of being able to live in luxury in Buckingham Palace and they are technically exempt from Criminal proceedings in Court! Not a bad deal really.