The Plessey Company plc was a British

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

-based international electronics, defence and telecommunications company. It originated in 1917, growing and diversifying into electronics. It expanded after the second world war by acquisition of companies and formed overseas companies. It was listed on the London Stock Exchange

London Stock Exchange

The London Stock Exchange is a stock exchange located in the City of London within the United Kingdom. , the Exchange had a market capitalisation of US$3.7495 trillion, making it the fourth-largest stock exchange in the world by this measurement...

 and was a constituent of the FTSE 100 Index

FTSE 100 Index

The FTSE 100 Index, also called FTSE 100, FTSE, or, informally, the footsie , is a share index of the 100 most highly capitalised UK companies listed on the London Stock Exchange....

 but in 1989 it was taken over by a consortium formed by GEC and Siemens

Siemens

Siemens may refer toSiemens, a German family name carried by generations of telecommunications industrialists, including:* Werner von Siemens , inventor, founder of Siemens AG...

 which broke up the Plessey group.
The Plessey company was founded in 1917 in Marylebone

Marylebone

Marylebone is an affluent inner-city area of central London, located within the City of Westminster. It is sometimes written as St. Marylebone or Mary-le-bone....

, central London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

.