Cities of London and Westminster (known as City of London and Westminster South from 1974 to 1997) is a constituency returning a single Member of Parliament (MP) to the House of Commons in the United Kingdom Parliament. It is a borough constituency for the purposes of election expenses and type of returning officer. As with all constituencies, the election is decided using the first past the post system of election. Since its creation at the 1950 general election, the constituency has always elected the candidate nominated by the Conservative Party.

Before 1950 the City of London formed a two-member constituency on its own. The Boundary Commission for England began reviewing constituencies in January 1946 using rules defined under the Representation of the People Act 1944, which excluded the City of London from the redistribution procedure;^[3][4] the Commission recommended that the borough of Chelsea and the City of Westminster form a single Parliamentary Borough of Chelsea and Westminster with two divisions.^[5]

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.^[6] During debates on the Bill, the Government amended it to substitute a link between the City of London and the City of Westminster.^[7] 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.^[8]

These changes came into force from the 1950 election.

1950–1974: From the Metropolitan Borough of Westminster: Charing Cross, Covent Garden, Great Marlborough Conduit, Grosvenor, Hamlet of Knightsbridge, Knightsbridge St. George, Pall Mall, Regent, St. Anne, St. John, St. Margaret, Strand.

In 1959, the boundaries changed, and the wards used instead were Abbey, Alderney, Aldwych, Berkeley, Cathedral, Churchill, Covent Garden, Dolphin, Eaton, Ebury, Grosvenor, Knightsbridge, Millbank, Regent Street, St. James's, Soho, Tachbrook, Victoria, Warwick and Wilton. In 1964, the City of Westminster was created to replace the old Metropolitan Borough of Westminster, which kept the same wards.

The City of London consisted of Aldersgate, Aldgate, Bassishaw, Bassishaw, Billingsgate, Bishopsgate, Bread Street, Bridge Within, Bridge Without, Broad Street, Candlewick, Castle Baynard, Cheap, Coleman Street, Cordwainer, Cornhill, Cripplegate, Dowgate, Farringdon Within, Farringdon Without, Langbourn, Lime Street, Portsoken, Queenhithe, Tower, Vintry and Walbrook.

In 1968, the City of Westminster ward boundaries changed, with the following used for this seat: Charing Cross, Churchill, Knightsbridge, Millbank, Regent Street, Victoria Street and Warwick.

1974–1983: The City of Westminster wards as above, and the City of London, as above.

New boundaries from 1978 meant the following wards from the City of Westminster were used: Baker Street, Belgrave, Bryanston, Cavendish, Churchill, Hyde Park, Knightsbridge, Millbank, St George's, St James's, Victoria, and West End.

In the City of London, Bridge Within and Bridge Without were combined in 1978 to create Bridge.

1983–1997: The City of Westminster wards as above, and the City of London as above.

1997–2010: The City of Westminster wards as above, plus, Bayswater and Lancaster Gate, and the City of London as above.

In 2002, a Local Government Boundary Commission for England review abolished the Baker Street, Belgrave, Bryanston, Cavendish, Knightsbridge, Millbank, St James's and Victoria wards.^[19]

For the 2005 general election, the Westminster electoral wards used in this constituency were Bayswater (part), Bryanston and Dorset Square (part), Churchill, Hyde Park, Knightsbridge and Belgravia, Lancaster Gate, Marylebone High Street, St James's, Tachbrook, Vincent Square, Warwick and West End.^[20]

2010–present: The City of Westminster 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, and the City of London wards, as above.

The seat covers the entire City of London and most of the City of Westminster lying South of the Marylebone Road and the Westway. In the latter, more residential, city it covers Westminster, Pimlico, Victoria, Belgravia, Knightsbridge, St. James's, Soho, most of Covent Garden, alongside parts of Fitzrovia, Marylebone, Edgware Road, Paddington and Bayswater.

The Cities of London and Westminster seat contains the two historical centres of the capital. The City of London is an international financial centre - while Westminster, home to the Buckingham Palace, Houses of Parliament, Whitehall and 10 Downing Street, represents Britain's political centre.

The seat includes iconic landmarks such as Buckingham Palace and St Paul's Cathedral, the West End's Theatreland and Soho. Some of the country's wealthiest residents live in exclusive Mayfair, Belgravia and Knightsbridge. Less than half the population was born in the UK - a fifth hail from elsewhere in Europe, while one in twenty is American, according to the 2011 Census.

Around half of the electorate are in the more socially mixed areas of Paddington and Pimlico, which includes some large council estates (Churchill Gardens and Millbank Estate).

The constituency also incorporates the wards of the City of London, some of which are the least populated wards in the United Kingdom, such as Coleman Street ward, which has a total electorate of 2, and Aldgate ward, which has a total electorate of 27.^[22]

Named Cities of London and Westminster from 1997 to date

• List of parliamentary constituencies in London