A global technology firm which started life as a family jeweller and clockmaker has celebrated 100 years as a listed company by opening the trading session of the London Stock Exchange today.

Smiths Group was first floated as S Smith Sons on July 21 1914, days before the outbreak of the First World War.

It is now one of the top 100 companies listed in London, with a market value of £4.8 billion and more than 23,000 employees in over 50 countries.

The firm had humble origins as a south London jewellery shop opened by Samuel Smith in 1851, before expanding into the West End and branching out into timepieces and car parts.

It pioneered the use of speedometers, fitting one of them to King Edward VII’s Mercedes and another for use by Captain Scott’s doomed expedition to the South Pole in 1912. By the time of the float, some 50,000 were estimated to be in use.

The company later adapted to munitions work during the First World War and aircraft instrument production in the Second World War.

It boasts that the maiden transatlantic flight, the conquest of Everest, the development of ultrasound scanners and autopilots and the first test tube baby also featured Smiths technology. Today its products cover a range of sectors from medical to security, including scanners used at airports.

The company marked a century since its float today as chief executive Philip Bowman signalled the start of trading from the balcony of the stock exchange.

He said: “Everyone at Smiths is immensely proud to be associated with a company that has not only reached this remarkable milestone but also created so much history as it repeatedly transformed itself to survive and prosper.

“Such a rich industrial heritage, allied to the business acumen and innovation that have sustained Smiths since Victorian times, affords us great confidence in tackling the challenges of the 21st century.”

The longest continually-listed company on the London stock exchange is Chilean-based FTSE 100 copper mining group Antofagasta.

It began as the Antofagasta (Chili) and Bolivia Railway Company plc, incorporated in London in 1888, later diversifying into mining and other sectors.