The four-storey London mansion hidden almost entirely underground: 15 bedrooms, 7 bathrooms, 20 toilets, a ballroom, a pool… and neighbours in uproar
David Graham’s home will feature 14-metre swimming pool and ballroom
Three-storey basement extension will be deeper than height of neighbouring houses and will treble size of the current Knightsbridge property
Novelist Edna O’Brien and other wealthy locals furious at plans