The Square, like much of London's prime real estate is the sole possession of the Duke of Westminster under the Grosvenor Estate banner and he occasionally grants us serfs such events as free classical music concerts, open air theatre and the free children's fun day.
In the nineteenth century the surrounding houses were pulled down to make way for Chesham and Balderton Buildings, as part of the Third Duke's plan to provide 'improved working-class dwellings'. As a result of this process a communal garden was placed down the centre for the residents.
However, when the electricity substation was built in 1902 the original garden had to be removed so, as compensation to the users of the garden, the paved area we see today was placed on the roof. This remained open until the 1980s when it was closed by the London Electricity Group. It reopened, however, in 2007 and remains open today.
For more information, visit http://www.brownhartgardens.co.uk