The first general post office in London opened in 1643, after King Charles I legalised use of the royal posts for private correspondence. It was possibly located on Cloak Lane near Dowgate Hill, in the City.
Later, in 1678, the General Post Office moved from Bishopsgate Street to a building in Abchurch Lane and remained there until the opening of this building on the east side of St. Martins-le-Grand in 1829, designed by Robert Smirke. Here Trollope began work as a junior clerk and here Rowland Hill transformed the Post Office into an efficient, greatly-loved institution.
Quoting from Mogg's New Picture of London and Visitor's Guide to it Sights, 1844, Victorian London describes this building and adds: "Here is the head of this vast establishment; but there are four branch offices, - at Lombard Street; Charing Cross; Cavendish Street, Oxford Street; and 266. Borough High Street."
In the 1870s a new building was created on the west of St Martins-le-Grand to house the telegraph department. This was expanded to the north in the 1890s. The magnificent Smirke building was closed and demolished in 1912. All that remains is an Ionic capital outside the Vestry House Museum in Walthamstow.
The National Telephone Company, created in 1881 out of a number of small local telephone companies, was taken over by the GPO in 1912.
The1870s building was the General Post Office headquarters 1894 - 1984.