The political centre of London is Westminster. It is the part of London where there are a lot of offices. 
If you go down Whitehall from Trafalgar Square on the right you will see a small street where the British Prime Minister lives. He lives at number 10, Downing Street. Whitehall is a wide street leading to Parliament Square. This square is very large.
On the left you can see a long grey building with towers which are the Houses of Parliament. The large clock in one of the towers is Big Ben. Big Ben is the name of the clock and the bell of the clock tower of the Houses of Parliament. You can hear the sound of Big Ben every hour in London. The clock and the bell got their names after Sir Benjamin Hall. He was a tall man, whose nickname was Big Ben. So people know the clock as Big Ben.
The Thames is behind the Houses of Parliament and the bridge across it is a Westminster Bridge.
On the other side of Parliament Square is Westminster Abbey. It is one the most famous and beautiful churches in London. It is very old too. It is more than nine hundred years old. There are so many monuments and statues there. Many English kings and queens are buried there.
 Westminster Abbey is famous for its Poet's Corner too. Many great writers are buried there: for example, Charles Dickens and Rudyard Kipling. The Queen of England lives in Buckingham Palace. It is a wonderful building with a monument in front of it which is the Queen Victoria Memorial. It takes twenty minutes to get from Trafalgar Square to Buckingham Palace.