The Palace of Westminster is the meeting place of the Parliament of the United Kingdom and is located in London, England. It is commonly called the Houses of Parliament after the House of Commons and the House of Lords, the two legislative chambers which occupy the building. The palace is one of the centres of political life in the United Kingdom; "Westminster" has become a metonym for the UK Parliament and the British Government, and the Westminster system of government commemorates the name of the palace. The Elizabeth Tower of the palace, nicknamed Big Ben, is a landmark of London and the United Kingdom in general. The palace has been a Grade I listed building since 1970 and part of a UNESCO World Heritage Site since 1987.