Plessey Former type Public company Industry Electronics, defence and telecommunications Fate Acquired (in 1989 by GEC/Siemens joint holding company – GEC Siemens plc) Successor GEC (1989–1999) Siemens Plessey (1989–1997) Marconi Communications (1998–2006) Siemens Communications (1998–2006) BAE Systems (1999 till date) Founded 1917 Defunct 1989 Headquarters Ilford, England Key people Sir John Clark (chairman)