Barbara Anne Castle, Baroness Castle of Blackburn, PC, GCOT (née Betts; 6 October 1910 – 3 May 2002) was a British Labour Party politician who was the Member of Parliament for Blackburn from 1945 to 1979, making her the longest-serving female MP in the history of the House of Commons until that record was broken in 2007 by Gwyneth Dunwoody. She later became the Member of the European Parliament for Greater Manchester from 1979 to 1989 and subsequently a member of the House of Lords, having been granted a life peerage in 1990.
One of the most significant Labour Party politicians of the 20th century, Castle developed a close political partnership with Harold Wilson and served in several Cabinet roles during both his premierships. As Minister of Transport (1965–1968) she oversaw the introduction of permanent speed limits, breathalysers and seat belts. Castle was then elevated to Secretary of State for Employment and First Secretary of State (1968–1970), and successfully intervened in the strike by Ford sewing machinists against pay discrimination. Following this Castle introduced the Equal Pay Act 1970. During her time in government Castle also served as Minister for Overseas Development and Secretary of State for Health and Social Services.