The seat was created by the Representation of the People Act 1918 and amounted to the larger, slightly less built-up part of the increasingly outer metropolitan Uxbridge seat which was split, in 1918, in two. It was given county seat status for unimportant logistical purposes. It amounted to the obsolete hundred plus the small west-to-east parishes in the north of Harmondsworth, Harlington and Cranford as the seat took in seven late 19th century-formed areas of local government, including the Staines Rural District. Due to the incursion into Elthorne Hundred the seat could have more accurately been named South West Middlesex.
