[4] The company was based in St Albans,[5] Colchester and Stevenage (where it eventually consolidated), all in southern England.

Prior to the consolidation in Stevenage, its main site was at Longacres[6] on the eastern outskirts of St Albans, where it was the largest employer.

There were four other sites, one at Hedley Road, one on Hatfield Road, St Albans (Fleetville Works), one on the Donibristle Industrial Estate in Fife, Scotland and one at Luton Airport, Luton.

The company operated an approved calibration and metrology laboratory for the electronics industry.

[citation needed] Marconi Instruments was sold to IFR Systems Inc. in 1998, itself acquired by Aeroflex in 2002.