From the Historic England entry:
“…It was in 1841 that the Threadneedle Street church, the only remaining non-conformist (in English church history, a Nonconformist was a Protestant who did not “conform” to the governance and usages of the established Church of England) French church in London, was obliged to give up its building, to allow for rebuilding in Threadneedle Street, and the congregation moved to a site in St Martin’s le Grand, remaining until 1887 when the church was demolished to make way for an extension to the headquarters of the General Post Office. Temporary quarters were found, first at the Athenaeum Hall in Tottenham Court Road, and then at a chapel behind 7 Soho Square, whilst the construction of the new church building was underway. A freehold site for the new church, then occupied by two houses, 8 and 9 Soho Square, was found, at a cost of £10,500. In March 1889 the consistory petitioned the Attorney General for permission to purchase the site and erect a new church accommodating a congregation of 400; permission was given in October 1890, the foundation stone was laid on 28 October 1891 and the building was dedicated on 25 March 1893. The architect chosen for the work was Aston (later Sir Aston) Webb (1849-1930), who in 1886 had redesigned the Victoria Law Courts, Birmingham, and in 1891 won the competition to complete the Victoria and Albert Museum; Webb’s designs for public buildings would include the Admiralty Arch (designed 1905-1907; built 1908-1911) and the re-fronting of Buckingham Palace (1913). Webb built few new churches, though he undertook a number of restoration projects. The French Protestant School in Great Marlborough Street (built in 1897-1898, now demolished) would also be designed by Webb. The builders of the church were Messrs Higgs and Hill, whose tender was for £10,194. A notice in The Builder (27 June 1891) notes an unusual feature of the design: ‘Owing to the nature of the site, hemmed in by houses, the church is nowhere displayed externally’. It has been suggested that discretion was a requirement of the design, but the principal reason for this is likely to have been practical: by being placed to the rear, the church is able to obtain light on three sides, whilst the presbytery and library are lit from the front. Certainly the design gives little outward indication of the function of the building, which looks more like an office building than a church. The existence of the French Protestant Church’s library is first mentioned in 1613-1615, when the church council minutes record the decision to collect subscriptions for ‘the establishment and erection of the library’. The material, housed in a dedicated library designed by Webb, now contains some 1400 early printed volumes; besides church records and manuscripts, are many books representing legacies, gifts, and acquisitions, reflecting the history and interests of the Huguenot congregation. In 1950 a carved panel by J Prangnelli was inserted into the tympanum above the main entrance, commemorating the 400th anniversary of the church’s foundation. The building has otherwise seen little significant alteration.
Today, the French Protestant Church in Soho Square, together with the Dutch Church in Austin Friars – rebuilt in 1950-1954 – survive as the direct descendants of the Strangers’ Church founded in 1550. The church in Soho Square is the only remaining French Protestant church in use in Britain, though regular services are held for French Protestants in the crypt of Canterbury Cathedral.”