If you have to understand the political system of a country, you will first have to learn about the history of that country. The history of the United Kingdom has been very much different from the rest of the world, and thus, its political systems are also quite different from the other countries.
The Britishers have been the greatest colonisers in the whole world. They never know how it is to be colonised and they also never had anything like the American Revolution or the French Revolution.
The three arms of the state:
The British political system is headed by the monarch, who is the head of the state. The current monarch of the UK political system is Queen Elizabeth II. But the most practical power will be the Member of the Parliament. The Member of the parliament seat is given to the person who got the most number of seats in the House of Commons. The powers of the monarchy are mostly ceremonial, but the members of the royal family do have some amount of influence on the legislative process.
The Executives are the ministers who run the country, and they are responsible for proposing new laws in the country.
The legislature is the body which is elected to pass the laws which are proposed by the executive.
The Judiciary consist of judges and the courts in the country that will be ensuring that everyone obeys the laws properly.
In the United Kingdom, there are strict divisions of these three arms and no one can be a part of two or more arms of the state. The separation of powers is followed, for example, the President of the country cannot be a member of the Congress.
The UK parliament:
The UK parliament is bicameral which means that there are two houses or chambers. The Parliament of the British is often called the Westminster as it is housed in a building in London and it is called the Palace of Westminster.
The house of the commons:
The house of the commons is the lower chamber, but it is the one with the most authority in the country. The speaker is the chair of the commons, and it currently has about 650 MPs (members of the Parliament). However, the seating capacity is only for 437 MPs. The Members of the Parliament have long benches where they would be seated.
The members of the Parliament of the commons represent a geographical constituency, and the constituency has about 60k to 80k voters. The number of votes depends on whether the area is urban or rural. The Isle of Wight has the most number of voters, and the smallest is from Na h-Eileanan. Every citizen who is above the age of 18 is eligible to vote.