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.