This series comprises the records of private telephone companies which were taken over by the Post Office in 1912. It consists of items relating to individual companies, National Telephone Company rules and instructions, staff related records, agreements, judicial proceedings, valuation of assets and a collection of early telephone directories.

Papers of Professor Silvanus Phillips Thompson, 1828-1951, comprising correspondence, 1828-1919, notably with William Edward Ayrton, 1883-1899; Sir William Fletcher Barrett, [1878-1896]; Antoine Henri Becquerel, 1902-1908; Alexander Graham Bell, 1879-1880, concerning his experiments with the telephone; Sir Wiliam Crookes, 1876-1916; Michael Faraday, 1830-1835 [written to Richard Phillips]; Sir William Huggins, 1879-1907; David Edward Hughes, 1884-[1912], concerning magnetism; Sir Joseph Larmor, 1902-1916; Sir Oliver Joseph Lodge, 1897-1919; Sir James Augustus Henry Murray, 1904-1913; Augusto Righi, [1902]-1916; William Thomson, 1882-1907; notes and printed material, [1907]-1951; photographs and prints, 1870-1910, notably photographs of friends and family.

The records of the Commonwealth Telecommunications Organisation reflect the history of Commonwealth co-operation in the field of international telecommunications. The collection is arranged into five general classes:

1. Imperial Communications Advisory Committee, 1928-1945
2. Commonwealth Communications Council, 1944-1949
3. Commonwealth Telecommunications Board, 1949-1969
4. Commonwealth Telecommunications Organisation (CTO), Commonwealth Telecommunications Council (CTC), and Commonwealth Telecommunications Bureau, 1966-1987
5. Commonwealth Telecommunications Organisation (CTO), Commonwealth Telecommunications Bureau and the Commonwealth Telecommunications Council (CTC) after 1987
   Each class represents the surviving records of the body that administered Commonwealth telecommunications relations during a particular period. Within each class, the material falls into three broad categories: the annual reports of the administrative body; the minutes, proceedings and memoranda of that body; the proceedings and minutes of committees and subcommittees appointed by the body. Most of this material is collected, by year, into bound volumes. In addition, the collection contains material (in files and bound volumes) that was not generated by the incumbent administrative body, but does relate to Commonwealth telecommunications during the lifetime of that institution and was presumably retained for use in the course of its activities or for reference purposes. Much of this material relates to the reports and proceedings of the Commonwealth Telecommunication Conferences under whose authority the administrative body derived its mandate. In each class, this material is listed under the heading General Documents.