In February 1948 the Government brought forward a new Representation of the People Bill which removed the right of owners of business premises to a second vote; this would have had the effect of reducing the electorate of the City of London from 12,500 to 4,600. The Bill proposed also to end the City of London as a separate constituency and to merge it with the adjacent boroughs of Finsbury and Shoreditch. During debates on the Bill, the Government amended it to substitute a link between the City of London and the City of Westminster. In introducing the amendment the Home Secretary James Chuter Ede noted that the alterations to the constituencies in Westminster, Chelsea and Kensington had been agreed unanimously at a conference between the Members of Parliament and representatives of the boroughs affected.
No alteration was made by the First Periodical Report on constituency boundaries in 1954. In the Second Periodical Report in 1969, the Boundary Commission wrote that their initial feelings were that "except for a minor alteration to follow a new ward boundary" they felt that there was "no reason to disturb" the constituency, and they received no objections to this proposal. Westminster City Council later suggested that the constituency could be more accurately named as 'The City of London and Westminster South'; the Boundary Commission found opinion divided and left the name unchanged when it published revised proposals for two other constituencies within the City. Subsequent representations on the name were received and the Commission decided that, although justified on historical grounds, the name was "not now entirely accurate" and so proposed the renaming as suggested by the City Council.
In initial proposals during the Third Periodical Review (1983), the Boundary Commission proposed to abolish the St Marylebone constituency and add four wards from it (Cavendish, Baker Street, Bryanston and Regents Park) to the previous City of London and Westminster South constituency; they provisionally named the result 'The City of London and Westminster'. After a local inquiry, the Regents Park ward was removed and Hyde Park ward (from the Paddington constituency) was added; unanimous opinion at the inquiry favoured naming the result 'The City of London and Westminster South'.
For the Fourth Periodical Review (1995), the Boundary Commission paired the City of Westminster with the Royal Borough of Kensington and Chelsea for consideration. The Commission's initial proposals, to expand the constituency by two wards (Bayswater and Lancaster Gate) formerly in Westminster North and to return to the name 'Cities of London and Westminster', were upheld after a local inquiry, despite multiple counter-proposals.
At the Fifth Periodical Review (2007), the initial proposals of the Boundary Commission paired the City of Westminster with the London Borough of Brent although they involved only minor changes to the Cities of London and Westminster constituency to take account of new ward boundaries. Widespread objections ("almost universal hostility") to the pairing led to a local inquiry, which decided that Westminster and the City of London should be reviewed separately and not paired with any other borough. The Commission proposed a new Cities of London and Westminster constituency in which the revised Bayswater and Lancaster Gate wards were removed.
Early proposals made during the abandoned Sixth Periodic Review of Westminster constituencies proposed linking the City of London to the southern wards of Islington in a constituency to be known as "The City of London and Islington South". Most of the Westminster wards were proposed to form part of a Westminster and Kensington constituency. This proposal was the first to suggest a split between the two Cities in Parliamentary elections since they were joined and proved unpopular in consultation; the Boundary Commission revised them to return the link between the City of London and the City of Westminster, although the whole review was subsequently abandoned.
Although united for Parliamentary elections, in the London Assembly, the City of London is covered by the City and East constituency, and the area in Westminster by the West Central constituency. The Local Government Commission for England argued that "combining the City of London with areas to its east could assist in focussing regeneration eastwards" and linked it with the London Borough of Tower Hamlets and the London Borough of Newham.
It is defined as the entire City of London, and the electoral wards of Bryanston and Dorset Square, Churchill, Hyde Park, Knightsbridge and Belgravia, Marylebone High Street, St James's, Tachbrook, Vincent Square, Warwick, and West End, in the City of Westminster.
From 1974 to 1983 the following City of Westminster wards were part of the constituency: Charing Cross, Churchill, Knightsbridge, Millbank, Regent Street, Victoria Street, and Warwick. From 1983 to 1997 the following City of Westminster wards were part of the constituency: Baker Street, Belgrave, Bryanston, Cavendish, Churchill, Hyde Park, Knightsbridge, Millbank, St George’s, St James’s, Victoria, and West End.