From the Wikipedia page 
Staines was a local government district from 1894 to 1974 around the town of Staines. Apart from Staines itself, it also covered Ashford, Laleham and Stanwell.
In 1894, under the Local Government Act 1894, Staines was created an urban district of Middlesex. It originally just covered the parish of Staines. In 1930 the parishes of Ashford, Laleham and Stanwell were added from the disbanded Staines Rural District. The Royal Commission on Local Government in Greater London considered the district for inclusion in Greater London. However in 1965, when Middlesex was abolished and its former area was transferred to Greater London under the London Government Act 1963, the Staines Urban District was instead transferred to Surrey.
In 1974, under the Local Government Act 1972, the urban district was abolished and its former area was combined with that of Sunbury-on-Thames Urban District to form the present-day borough of Spelthorne.