Barbara Castle, Baroness Castle of Blackburn, English politician, First Secretary of State (b. 1910)
Barbara Anne Castle, Baroness Castle of Blackburn, (née Betts; 6 October 1910 – 3 May 2002), 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.

A graduate of the University of Oxford, Castle worked as a journalist for both Tribune and the Daily Mirror, before being elected to Parliament as MP for Blackburn at the 1945 election. During the Attlee Government, she was Parliamentary Private Secretary to Stafford Cripps, and later to Harold Wilson, marking the beginning of their partnership. She was a strong supporter of Wilson during his campaign to become Leader of the Labour Party, and following his victory at the 1964 election, Wilson appointed Castle to the Cabinet as Minister for Overseas Development, and later as Minister of Transport. In the latter role, she proved an effective reformer, overseeing the introduction of permanent speed limits for the first time on British roads, as well as legislating for breathalyser tests and compulsory seat belts.

In 1968, Wilson promoted Castle to become First Secretary of State, the second-most senior member of the Cabinet, as well as Secretary of State for Employment. In the latter role, Castle fiercely advocated for the passage of the In Place of Strife legislation which would have greatly overhauled the operating framework for British trade unions. The proposal split the Cabinet, and was eventually withdrawn. Castle was also notable for her successful intervention over the strike by Ford sewing machinists against gender pay discrimination, speaking out in support of the strikers, and overseeing the passage of the Equal Pay Act. After Labour unexpectedly lost the 1970 election, some blamed Castle's role in the debate over trade unions for the defeat, a charge she resisted.

Upon Labour's return to power after the 1974 election, Wilson appointed Castle Secretary of State for Health and Social Services, during which time she was responsible for the creation of Carer's Allowance and the passage of the Child Benefit Act. She was also a prominent opponent of Britain's continued membership of the European Economic Community during the 1975 referendum. When Castle's bitter political rival, James Callaghan, replaced Wilson as Prime Minister in 1976, he sacked her immediately from the Cabinet; the two would remain bitter towards each other for the rest of their lives. Opting to retire from Parliament at the 1979 election, Castle quickly sought election to the European Parliament, representing Greater Manchester from 1979 to 1989; during this time, she was the Leader of the European Parliamentary Labour Party from 1979 to 1985, and publicly reversed her previous stance of Euroscepticism. She became a member of the House of Lords, having been granted a life peerage, in 1990, and remained active in politics until her death in 2002 at the age of 91.