The Plessey Microsystems division was the subject of a management buyout in 1988[1][2] becoming Radstone Technology, which survives today as part of Abaco Systems based in Towcester, Northamptonshire.

The bulk of Plessey's telecommunications assets were acquired by Ericsson through its 2005 acquisition of Marconi Communications, a successor company of GEC.

Important contracts included the manufacture of early radios[3] for Marconi and the production of telephones for the General Post Office.

In 1936, Plessey obtained a number of important manufacturing licences from American companies such as Breeze Corporation for aircraft multi-pin electrical connectors, Federal Laboratories for Coffman starters (an explosive cartridge device used to start aircraft engines), and Pump Engineering Services Corporation for the manufacture of Pesco fuel pumps.

To allow greater production, Plessey converted five miles of twin tunnel, built for a new extension to the London Underground Central line from Leytonstone to Newbury Park, into a factory.

Radio and television sales were the main area of activity until the renewed demand for defence products with the onset of the Korean War.

Plessey produced an early integrated circuit model in 1957, before the patents of Jack St. Clair Kilby of Texas Instruments and Robert Noyce of Fairchild.

[5][6][7] In the 1960s the Group continued to expand, setting up facilities at places such as West Leigh (Havant, Hampshire) and Templecombe, Somerset.

In 1970, the Command and Control unit was set up at Christchurch, Dorset, which became the centre of the Plessey Defence Systems business.

In 1979, a major subsidiary was set up, Plessey Electronic Systems, which incorporated the three businesses and by 1986 achieved sales of over £500 million and employed 15,000.

Their Training Department developed an interactive management game (PITDEX) using TeleType printer/keyboards to link to LEASCO computers in the United States via standard telephones and acoustic couplers.Plessey also pioneered the gathering and consolidation of accounting information from around the world using in-house software.

[3] A division focused on microcomputing, Plessey Microsystems, was founded in 1975, having licensed the 16-bit Miproc processor architecture developed by the Norwegian Defence Research Establishment and Aksjeselskapet Mikro-Elektronikk.

[11] During the 1970s and early 1980s, Plessey manufactured a series of computer systems and peripherals compatible with Digital Equipment Corporation's PDP-11, some based on the Miproc product which was itself revised to operate with a faster 250ns cycle time.

In 1959 AT&E, later Plessey, became the prime contractor for a new UK air defence system, known by the company under the name Plan Ahead and, from 1961, as Project Linesman.

[14] The secure status of the factory attracted many other secret contracts and led to it becoming one of the major designers and manufacturers of cryptographic equipment.

[3] At the time, IMC was in the process of industrialising a unique South African invention, the Tellurometer, the first successful microwave electronic distance measurement equipment.

[15] The instrument was invented by Dr. Trevor Lloyd Wadley of the Telecommunications Research Laboratory of the South African Council for Scientific and Industrial Research (CSIR), also responsible for the Wadley loop receiver, which allowed precision tuning over wide bands, a task that had previously required switching out multiple crystals.

In 1989, when GEC-Siemens took control of the Plessey Company, Sankorp indicated its intention to purchase the remaining 74% of shares in the South African subsidiary.

In the 1970s and 80s it produced Ericsson Crossbar Telephone Exchanges under licence for Telecom Australa and the PNG Post and Telegraphs department.

[citation needed] In December 1985, GEC launched a takeover bid for the Plessey Company, valuing the group at £1.2 billion.

In 2011/2, Plessey acquired the rights to disruptive GaN-on-silicon technology by acquisition of CamGaN, a startup company, from Cambridge Enterprises.

[33] Plessey continues to operate in the Roborough site[34] with leading-edge 150mm and 200mm wafer processing facilities to undertake design, test and assembly of products, and a comprehensive suite of photonic characterisation and applications laboratories.

They have now upgraded to full-field emissive microLED displays that combine very high-density RGB pixel arrays with high-performance CMOS backplanes to produce very high-brightness, low-power and high-frame-rate image sources.

PTSA continued to grow with a strong focus on telecommunications and defence products, particularly with a major expansion into large projects, rolling out the microwave backbone of MTN, one of South Africa's first GSM cellular networks and the installation of a fibre optic network and radio broadcasting system in Malaysia.

A software division was formed through the acquisition of BSW data, largely staffed by engineers from the recently terminated South African space programme in which PTSA had also participated, both in the electronics of the launch vehicle and the satellite itself.

The full acquisition of AWA-Plessey Communications, which Plessey jointly owned in Australia with Amalgamated Wireless (Australasia) Ltd (AWA) and had a similar product portfolio, resulted in penetration into the Pacific Rim market.

The culmination of this growth was the company's listing on the Johannesburg Stock Exchange (JSE) as the Plessey Corporation in the same year.

[3] On the evening of 6 February 1996, a devastating fire swept through two bays of the White Road factory in Retreat, Cape Town causing huge damage to stock, instruments, plant and work in progress.

The remaining divisions, notably with a product development and manufacturing focus, were bought back by a combined management buyout supported by Rand Merchant Bank.

The name is also used to refer to a barcode symbology developed by Plessey, which is still used in some libraries and for shelf tags in retail stores, in part as a solution to their internal requirement for stock control.