thumb|250px|Standard of Lord Protector [[Oliver Cromwell]]

Lord Protector (plural: Lords Protector) is a title that has been used in British constitutional law for the head of state. It was also a particular title for the British heads of state in respect to the established church. It was sometimes used to refer to holders of other temporary posts; for example, a regent acting for the absent monarch.

Feudal royal regent

The title Lord Protector was originally used by royal princes or other nobles exercising a role as protector and defender of the realm, while also sitting (typically as chairman) on a regency council, governing for a monarch who was unable to do so (on account of minority, absence from the realm on Crusade, mental incapacity, etc.).

Notable cases in England:

  • John of Lancaster, Duke of Bedford, and Humphrey, Duke of Gloucester, were (5 December 1422 – 6 November 1429) jointly Lords Protector for Henry VI (1421–1471);
  • Richard Plantagenet, Duke of York, was three times (3 April 1454 – February 1455; 19 November 1455 – 25 February 1456; and 31 October – 30 December 1460) Lord Protector for Henry VI;
  • Richard, Duke of Gloucester, was "Lord Protector of the Realm" (10 May 1483 – 26 June 1483) during the nominal reign of Edward V (one of the Princes in the Tower) before being offered the throne as Richard III;
  • Edward Seymour, Duke of Somerset, was Lord Protector (4 February 1547 – 11 October 1549) during the early years of the reign of the young Edward VI;

and in Scotland:

  • John Stewart, Duke of Albany, was "Governor and Protector of the Realm" (12 July 1515 – 16 November 1524) for James V of Scotland (1512–1542);
  • James Hamilton, Duke of Châtellerault, was "Governor and Protector of the Kingdom" (3 January 1543 – 12 April 1554) for Mary, Queen of Scots.

Cromwellian Commonwealth

The Lord Protector of the Commonwealth of England, Scotland and Ireland was the title of the head of state and head of government during the Commonwealth (often called the Interregnum), following the first period when a Council of State held executive power. The title was held by Oliver Cromwell (December 1653 – September 1658) and subsequently his son and designated successor Richard Cromwell (September 1658 – May 1659) during what is now known as The Protectorate.

The 1653 Instrument of Government (republican constitution) stated:

The replacement constitution of 1657, the Humble Petition and Advice,