Telegraph Construction and Maintenance Co
of 22 Old Broad Street, London, EC2. Works at Greenwich, London, SE10. Telephone: GREenwich 1040. Telegraphic Address: "Moorings, Green, London". (1937)
Ditto Address. Telephone: London Wall 3141. Cables: "Telcon, Stock, London". (1947)
The company made the 1865 and 1866 transatlantic cables and (as its forerunner Glass, Elliot and Co), the 1857 and 1858 cables.
1900 The company's tender for the Pacific Cable Co was accepted; the cable was laid across the Pacific by Nov 1902
1903 Map: Telegraph Construction and Maintenance Co Ltd - Showing submarine telegraph cables the cores of which were manufactured at The Gutta Percha Works, Wharf Road, City Road, London, N. 
1914 Manufacturers, layers and repairers of submarine telegraph cables. 
1924 Invented and patented MUMETAL® high permeability alloy.
1935 Submarine Cables Ltd was formed by Siemens Brothers and Co and Telegraph Construction and Maintenance Co when, because of the Depression, there was insufficient work for the submarine cable divisions of the 2 companies.
1937 British Industries Fair Advert for 'Telcon' Cables; Magnetic Alloys; Heat Resisting Alloys; Gutta Percha products. Manufacture and Laying of Impregnated Paper Insulated Cables. Broadcast Relay Cables. Cables for Television and High Frequencies. Magnetic and Heat-resisting Alloys. Gutta Percha Moulded Goods of every description. (Electricity: Industrial and Domestic Section - Stand No. Cb.503) 
1937 Cable manufacturers (P.I.I.C. for power distributors). "Radiometal" Alloy. "Rhometal". "2129" Alloy. 
1947 Listed Exhibitor - British Industries Fair. Manufacturers of High and Radio Frequency and Television Cables, Radio Relay Cables, Thermoplastic Cables. Magnetic, Resistance and Glass Sealing Alloys, Thermostatic Bimetals, Invar, Beryllium Copper. Thermoplastic Mouldings, Road, Sheets, Tubes. (Olympia, Ground Floor, Stand No. C.1524) 
1951 Joint sales venture Telcon Telecommunications Ltd formed with Mullard Electronic Products to promote and coordinate the development manufacture and sales of Telcon cables and Mullard electronic products associated with land line equipment
1959 Was absorbed by BICC.
1961 Manufacturers of paper insulated power cables, radio frequency and television cables, land communication cables, magnetic and electrical resistance alloys, veryllium copper aged hardening alloys "Telcothene" and gutta percha thermoplastics. 
Sources of Information
- The Stock Exchange Year Book 1908
- The Engineer 1869/06/18
-  Shipping Times
- The Times Nov. 1, 1902
-  History of the Atlantic Cable and Submarine Telegraphy
- 1914 Whitakers Red Book
- Telcon history: 
- The Engineer 1926/01/22
- 1937 British Industries Fair Advert p587
- 1937 The Aeroplane Directory of the Aviation and Allied Industries
- 1947 British Industries Fair p273
- The Times, Mar 05, 1951
- 1961 Dun and Bradstreet KBE