 The line to Windsor through Middlesex was completed in 1848, and the railway to Potters Bar in 1850; and the Metropolitan and District Railways started a series of extensions into the county in 1878.Closer to London, the districts of Acton, Willesden, Ealing and Hornsey came within reach of the tram and bus networks, providing cheap transport to central London.After World War I, the availability of labour and proximity to London made areas such as Hayes and Park Royal ideal locations for the developing new industries.