Dartford is a constituency represented in the House of Commons of the UK Parliament since 2010 by Gareth Johnson of the Conservative Party. It is currently the longest-valid 'bellwether' constituency in the country as the party of the winning candidate has gone on to form the government at every UK general election since 1964. Candidates for the largest two parties nationally have polled first and second since 1923 in Dartford. The area in the seat, remaining a combination of urban, suburban and a small rural population, has been gradually reduced through contribution to new seats, their county designation later being changed in 1965 to become part of the new county of Greater London, which adjoins. These seats are Bexley, created in 1945 and Erith & Crayford, created in 1955. History The seat was created under the Redistribution of Seats Act 1885. This Act added a net 18 seats, but its main purpose was to correct the over-representation of minor, often still old boroughs and depopulated county divisions. In their place were created new seats with a larger population. In Kent the Act finally abolished the Sandwich constituency, which sent two MPs until 1885. It also halved the representation of no fewer than four other historic towns. In contrast a seat for Dartford, the North-Western Division of Kent or North West Kent, was created. Political history In the early 20th century, the Dartford constituency was very much a bellwether. Dartford's results later shifted towards the left: in a by-election in 1938 and then general elections from 1951 to 1959, a Labour MP was elected against the national result. Since 1964, however, Dartford has alternated between Labour and the Conservatives in line with the national result, and thus has served as a bellwether again. This was the first seat contested by future Prime Minister Margaret Thatcher (then Margaret Roberts), at the 1950 and 1951 general elections. She was unsuccessful on both occasions, with Labour retaining the seat and being re-elected to government in 1950; only to lose power to the Conservatives a year later. Boundaries 1885–1918: The Sessional Division of Dartford, and part of the Sessional Division of Bromley. 1918–1945: The Urban Districts of Bexley, Dartford, and Erith, and in the Rural District of Dartford the parishes of Crayford, Stone, and Swanscombe. 1945–1955: The Boroughs of Dartford and Erith, and the Urban District of Crayford. 1955–1974: The Borough of Dartford, the Urban