Later Occupancy and Use of 15 Kensington Gardens
In his Will George Moore left in 1876 the leasehold Mansion House and its grounds and contents to his widow, Jane Agnes who died herself in 1888. I have not been able, at this point in time, to ascertain whether the property remained in her possession until her death or, indeed, who occupied the property after the Moore family. If anyone has information, please contact me. 
I do know that no significant alterations were made to No. 15 until 1937–8, when parts of the interior were completely remodelled by Lord Gerald Wellesley and Trenwith Wills for Sir Alfred Beit, the financier and philanthropist. In 1939, following a short engagement, Sir Alfred married Clementine Mitford, a great beauty and first cousin to the much publicized Mitford sisters. Sir Alfred and Lady Beit made their home at 15 Kensington Palace Gardens, which Sir Alfred had bought and remodelled to accommodate his collection of paintings, bronzes, furniture and other treasures. Unfortunately, the Second World War was to start just months after Sir Alfred’s marriage to Clementine and during the bombing of London, their house was damaged. Sir Alfred sold 15 Kensington Palace Gardens sometime after the war, I think, around 1952 when the Beits moved to Russborough House in Ireland.
In the 1970s No 15 was occupied by the Iraqi Ambassador.
In the 1990s No 15 became an annexe of the Russian Embassy next door and reputedly served as a base for Moscow's intelligence services.
In 2004 Len Blavatnik, a Jewish-American industrialist, born in Russia and currently living in New York and London, purchased the 15-bedroom villa at 15 Kensington Palace Gardens with a neighbouring building for £41m. In the Sunday Times Rich List 2006 he was listed as the sixth richest person in the UK with an estimated fortune of £4,670m.
The transaction was seen as part of an attempt by the Crown Estate, the freeholder of the street which neighbours Kensington Palace, former home of Diana, Princess of Wales to transform the area from diplomat's row to billionaire's boulevard. The building is next to the Russian embassy and across the road from the official residence of the ambassador of Finland. The presence of these and other diplomatic missions such as the Israeli embassy means the street is regularly patrolled by armed police and private security guards who, the residents hope, deter most burglars.
Those familiar with the house, designed by the architect James Knowles in 1854, said the new owner, Len Blavatnik, would need to spend about £7m to restore it. During its period as a Russian property, the faded wallpaper, frayed carpets and 1970s-era swivel chairs are said to have given the building a dingy ambience. One former visitor said: "It has eerie basements with swinging lights, which are a bit scary."
While 15 Kensington Palace Gardens was discreetly marketed for £35m, the buyer is also understood to have paid £6m for Cope House, the former stable block, in its grounds. Cope House had been for sale since 1998 after its then owner, Wensley Haydon-Baillie, a selfmade pharmaceuticals tycoon, went bankrupt.
The street's transformation back into a residential enclave began when the Sultan of Brunei took a long lease on a property there in 1991 for £18m. Bernie Ecclestone, the Formula One tycoon, also owns a house in the street, which he bought for £50m and has been trying to offload for a reputed £85m.
Underground house extensions, it seems, are quite the vogue with the city's ineffably rich. Only recently, Jon Hunt, founder of the estate agents, Foxtons, who sold the business for £390m, revealed his plan to burrow beneath the house he paid £14m for some years ago in Bling Row (Kensington Palace Gardens, an avenue of miniature 19th-century palaces inhabited by business magnates and embassies) to build a four-storey gym, swimming pool and a museum for his collection of Ferraris. Not to be outdone, one of his close neighbours, the oil-rich Russian Leonid Blavatnik has commissioned David Cameron's favourite architects, Michaelis Boyd, to design an equally ambitious sports centre beneath his modest £41m home. All very green and eco-friendly, of course!
In the Summer of 2010 I visited Kensington Palace Gardens and found that extensive building work and refurbishment work was being undertaken at No 15. I spoke briefly to two gentleman I met leaving the property, one of whom introduced himself as an historical researcher for the present owner. He told me that he was aware that the house had been built for and originally occupied by George Moore. This encounter prompted me to write to Mr Blavatnik asking if his office was able to provide me with any historical information about the property and suggesting to him that it would be most fitting to apply to the Commissioners for a blue plaque to be fitted to the house to record George Moore's occupancy. I received a prompt and polite, if somewhat curt reply to the effect that the present owner was unable to assist me in these matters.
Partly from: 'The Crown estate in Kensington Palace Gardens: Individual buildings', Survey of London: volume 37: Northern Kensington (1973).
History of the Area : George Moore's neighbours : George Moore's Mansion House