The Grade II-listed late Victorian building, built as one of the early mansion blocks in the English capital, is thought to be named after an ancient monastery reputed to have occupied the site pre-10th century.

Converted to a hotel in 1896–1899, it became during the 1930s, through the Second World War and beyond, a meeting place of the British intelligence services, notably the birthplace of the Special Operations Executive (SOE),[3] and where notorious Cambridge Five double agents Philby and MacLean met their Russian handlers.

St Ermin's Mansions was typical in both plan and elevation; Hall employed the fashionable red-brick Queen Anne style for the exterior and grouped the apartments around a courtyard, which functioned both as a carriageway and garden for the residents.

[6] The new owners embarked on a major refurbishment programme undertaken by the theatre architect J. P. Briggs (1869–1944),[7] providing a spectacular sequence of public reception rooms with very rich plasterwork.

Briggs remodelled the far end of the courtyard, creating a neo-Baroque space with raised verandah leading into a double-height foyer dominated by an undulating balcony at gallery level, accessed via a double staircase.

Next door the hotel has the Caxton Hall, built in 1882–1883, famous for the first meeting of the Suffragette Movement in 1906, infamous for the revenge assassination of Michael O'Dwyer in 1940 and a celebrity civil marriage venue in the 1950s and '60s – Roger Moore, Peter Sellers, Diana Dors and Elizabeth Taylor all took their vows there, some more than once.

[12] Shortly before the war the hotel was the venue for guerrilla warfare classes run partly by MI6, and among those working for 'King and Country' within that group at the time was Noël Coward, as well as art expert and member of the Cambridge Five spy ring, Anthony Blunt.

The group was created following the conference decision to establish an electoral college (40% trade unions, 30% members, 30% MPs) to elect the Labour Party leader and deputy.