The Urban District of Potters Bar, and the Urban District of Enfield wards of South West and West.
Potters Bar Urban District (comprising that town, South Mimms and North Mimms, namely the western half of the seat) became part of Hertfordshire in 1965 however no change was made then to Westminster representation. The other district's wards having also been Middlesex became parts of Greater London, under the same Act passed in 1963 following a Royal Commission.[1]