 In April 1965, nearly all of the area of the historic county of Middlesex became part of Greater London, under the control of the Greater London Council, and formed the new outer London boroughs of Barnet (part only), Brent, Ealing, Enfield, Haringey, Harrow, Hillingdon, Hounslow and Richmond upon Thames (part only).The remaining areas were Potters Bar Urban District, which became part of the administrative county of Hertfordshire, and Sunbury-on-Thames Urban District and Staines Urban District, which became part of the administrative county of Surrey.Following the changes, local acts of Parliament relating to Middlesex were henceforth to apply to the entirety of the nine "North West London Boroughs".