Barbara Anne Castle, Baroness Castle of Blackburn, was a British Labour Party politician who was a Member of Parliament from 1945 to 1979, making her one of the longest-serving female MPs in British history. Regarded as one of the most significant Labour Party politicians, Castle developed a close political partnership with Prime Minister Harold Wilson and held several roles in the Cabinet. She remains to date the only woman to have held the office of First Secretary of State.

The 1945 United Kingdom general election was a national election held on Thursday 5 July 1945, but polling in some constituencies was delayed by some days, and the counting of votes was delayed until 26 July to provide time for overseas votes to be brought to Britain. The governing Conservative Party sought to maintain its position in Parliament but faced challenges from public opinion about the future of the United Kingdom in the post-war period. Prime Minister Winston Churchill proposed to call for a general election in Parliament, which passed with a majority vote less than two months after the conclusion of the Second World War in Europe.