Plessey

The Plessey Company plc was a British electronics, defence, and telecommunications company. It was listed on the London Stock Exchange and was part of the FTSE 100 Index until it was bought by GEC and Siemens in 1989.

Plessey started in 1917, focusing on mechanical engineering. In the 1920s, it began making electronics, such as radios for Marconi and telephones for the General Post Office. During World War II, Plessey helped the British war effort by using underground tunnels originally built for the London Underground.

During the Cold War, Plessey grew by buying other companies and creating subsidiaries abroad. In 1961, it merged with Ericsson Telephones and the Automatic Telephone Manufacturing Company to become Britain’s largest maker of telecommunications equipment. Plessey helped develop important technologies like the Atlas computer and the System X digital telephone system.

In 1989, GEC and Siemens took over Plessey, splitting its assets. Many of its defence parts became part of BAE Systems. Today, the Plessey name lives on in a company that makes optical semiconductors.

History

The Plessey company started in 1917 in Marylebone, London. The founders were Thomas Hurst Hodgson, C. H. Whitaker, Raymond Parker, and his brother Plessey Parker. A skilled German engineer, William Oscar Heyne, joined the company and became a key leader in its growth during the 1920s and 1930s. The company moved to Ilford in 1919.

In the 1920s, Plessey began making electrical products. They made early radios for Marconi and telephones for the General Post Office. In 1923, they moved to a new location in Ilford to make more products. By the 1930s, Plessey started making parts for airplanes.

During the Second World War, Plessey made many parts and tools for the war effort, including pieces for airplanes and radios. They used tunnels under construction for a London Underground line to make these items and opened new factories around the country.

After the war, Plessey continued to grow. They made radios and televisions until the Korean War brought more demand for defense products. In the 1950s, they began making early computer parts and set up research centers. They also made telephone systems and other communication tools.

Plessey became a big maker of telecommunications equipment after merging with other companies in the 1960s. They were involved in developing early computers and communication systems. In the 1970s and 1980s, they made computer systems and tools for measuring radiation.

In the 1980s, there were attempts to take over Plessey by other companies, but these were blocked. Finally, in 1989, Plessey was taken over by a joint venture between GEC and Siemens.

Break-up of the business

In April 1990, GEC and Siemens agreed on a new way to share the Plessey businesses.

GEC acquisitions

• In the UK
  • Plessey Aerospace
  • Plessey Avionics
  • Plessey Crypto
  • Plessey Materials
  • Plessey Naval Systems
  • Plessey Semiconductors
  • Plessey Research Caswell
  • Plessey Microsystems
  • Plessey Controls
• In North America
  • Plessey Aero Precision Corp
  • Plessey Dynamics Corp
  • Plessey Electronic Systems Corp (including ES Marine Systems)
  • Sippican
  • Plessey Materials
  • Leigh Instruments

Siemens acquisitions

• Siemens Plessey Radar
• Siemens Plessey Defence Systems
• Siemens Plessey Controls
• Siemens Plessey Australia
• Siemens Plessey Assessment Services
• Roke Manor Research

Jointly owned

• GEC Plessey Telecommunications: 60% GEC and 40% Siemens

Disposals

• Birkby Plastics (1989–1990)
• Hoskyns Group
• Plessey Valdarno S.p.A. (Italy), sold to Magnetek in 1991
• 51% share in Plessey Telenet acquired by minority partner in 1992
• 74% share in Plessey South Africa acquired by minority partner Sankorp

Subsequent history

UK

In October 1997, British Aerospace and DaimlerChrysler Aerospace took over the UK operations and the German part of Siemens Plessey Systems.

By 1997, the GPT name was no longer used in the UK, and the company became known as Siemens GEC Communication Systems (SGCS), which later changed to Siemens Communications. In August 1998, GEC bought Siemens' share in GPT and merged it with other telecom units to form Marconi Communications. In December 1999, GEC's defence part Marconi Electronic Systems joined with British Aerospace to create BAE Systems.

The rest of GEC was renamed to Marconi plc, with Marconi Communications as its main part. The company struggled because of the dot-com bubble and was reorganised into Marconi Corporation in 2003. Two years later, most of the company (including Marconi Communications) was purchased by Ericsson, and the rest became Telent.

The part of GPT that became Siemens Communications later turned into Siemens Enterprise Communications in 2008.

GEC Plessey Semiconductors (GPS) was bought by Mitel Semiconductors of Canada in 1998. After some reductions, including the sale of the power semiconductor and silicon on sapphire operation at Lincoln, Lincolnshire to Dynex Semiconductor in 2000, the company renamed itself Zarlink Semiconductor in 2001. The GPS factory in Plymouth was sold to Xfab in March 2002.

Plessey Semiconductors Ltd

After selling the Roborough site in Plymouth to Xfab, the original Plessey Semiconductors site in Swindon kept operating under the Zarlink Semiconductor name until it was sold to MHS Industries in early 2008. In February 2009, the UK business was forced into receivership after the parent MHS Electronics business in France collapsed. After a management buyout, the company started trading as Plus-Semi Ltd.

The Roborough site (8" and 6" lines) was bought back from Xfab on 1 January 2010, and the company was renamed Plessey Semiconductors Ltd. The new company moved its bipolar processes on silicon and SOI to the 8" Plymouth factory in 2010, using the combined technology to develop new processes and products for various markets. The Swindon site was torn down in July 2012. In 2011/2, Plessey bought the rights to GaN-on-silicon technology by purchasing CamGaN, a startup from Cambridge Enterprises.

Using GaN-on-silicon technology and semiconductor skills, Plessey Semiconductors Ltd made solid state lighting, horticultural lighting, and medical sensing products. Their GaN-on-silicon i2LED high power LEDs and Stellar Orion beam forming modules, launched in autumn 2016, allowed new designs for lighting products and removed design limits for lighting product creators. In horticulture, the Plessey Attis Growlight led to a new brand, Hyperion Grow Lights. The company's medical products using the EPIC sensor were used in the portable ECG monitor, Impulse, and also formed the basis of an R&D program called Warden to develop devices to monitor driver alertness in cars and airplanes.

In 2017, Plessey shifted focus to research and making microLEDs (micro light-emitting diodes) as a new display technology for many uses, including augmented reality, mixed reality, smartphones, TVs, smartwatches, head-up displays, and head-mounted displays.

Plessey still works at the Roborough site with facilities for 150mm and 200mm wafer processing to design, test, and assemble products, along with labs for photonic characterisation and applications.

Their first microLED product was a light for display engines (DMD and LCOS), which made the light engine 40% smaller while using more energy efficiently. Later, full-screen microLED displays combine high-density RGB pixel arrays with high-performance CMOS backplanes to create bright, low-power, and high-frame-rate images. These new products have won industry awards like the Elektra Awards 2017, British Engineering Excellence Awards 2017, National Technology Awards 2018, CES Innovation Awards 2019, and Electronics Industry Awards 2019.

In March 2019, Plessey used their GaN-on-silicon technology, which naturally makes blue light, to change the early layers to make green light, opening more chances for markets like military use. Plessey also achieved the world's first GaN-on-silicon monolithic wafer-to-wafer bonding.

In August 2025, Plessey Semiconductors was bought by Haylo Labs, using money from Chinese AI smartglasses maker Goertek Inc. The purchase got national security approval after a review under the National Security and Investment Act 2021.

South Africa

In South Africa, after the GEC/Siemens takeover, Plessey South Africa became fully owned by Sankorp and was renamed Plessey Tellumat South Africa Limited (PTSA). The name Tellumat had two meanings: it showed the company's focus on exports, as it was the name of its UK export part, and it came from the Tellurometer, South Africa's first electronic surveying tool—showing a commitment to electronic research and development.

PTSA kept growing with a strong focus on telecommunications and defence products, especially by working on big projects, like setting up the microwave network for MTN, one of South Africa's first GSM mobile networks, and installing a fibre optic network and radio system in Malaysia. A software part was created by buying BSW data, mostly using engineers from South Africa's space programme, where PTSA also helped with the electronics of the rocket and the satellite.

1995 was a big year for the company in South Africa. The merger of PTSA and Tek Electronics, a consumer electronics audio and video products maker and seller (also fully owned by Sankorp), brought the business back to its roots in consumer electronics. This led to PTSA being renamed back to the original Plessey South Africa Limited. The full purchase of AWA-Plessey Communications, which Plessey jointly owned in Australia with Amalgamated Wireless (Australasia) Ltd (AWA) and had similar products, helped the company enter the Pacific Rim market. The growth reached its peak when the company listed on the Johannesburg Stock Exchange (JSE) as the Plessey Corporation in the same year. Shares started at R4.80 each. On the evening of 6 February 1996, a big fire damaged two parts of the White Road factory in Retreat, Cape Town, ruining stock, tools, equipment, and work in progress. No one was hurt, but work stopped for several weeks. Large parts of the factory had to be rebuilt.

At the end of 1996, Plessey Corporation sold the sales and marketing part of Telefunken, Pioneer, and Satellite TV.

In August 1998, Plessey Corporation was bought by Dimension Data Holdings and Worldwide African Investment Holdings for R1.6 billion. The new owners kept BSW Data, Plessey Solutions, and Communications Systems. The other parts, which focused on product development and making, were bought back by a management buyout supported by Rand Merchant Bank. The company name changed to Tellumat Pty Ltd. Tellumat still makes and sells Plessey-branded products as before and works in the defence, telecommunications, and contract manufacturing markets.

Plessey barcodes

The name also refers to a special kind of barcode made by Plessey. This barcode is still used in some libraries and stores to help keep track of items on shelves. It started being used in the early 1970s by J.Sainsbury to make sure they could restock their products easily.

One good thing about this barcode is that it was easy to print with the printers popular at the time. It also fits more information in a smaller space than some other codes. The barcode uses two different widths of bars, with the wider bar acting as a start and two narrow bars as a stop. The bars in between come in groups of four, with narrow bars meaning 0 and wide bars meaning 1.