Queen Anne withheld royal assent from the Scottish Militia Bill, in the most recent veto by a British monarch of a bill that had been passed by Parliament.

Anne was Queen of England, Scotland, and Ireland from 8 March 1702, and Queen of Great Britain and Ireland following the ratification of the Acts of Union 1707 merging the kingdoms of Scotland and England, until her death in 1714.

Royal assent is the method by which a monarch formally approves an act of the legislature, either directly or through an official acting on the monarch's behalf. In some jurisdictions, royal assent is equivalent to promulgation, while in others that is a separate step. Under a modern constitutional monarchy, royal assent is considered little more than a formality. Even in nations such as the United Kingdom, Norway, the Netherlands, Liechtenstein and Monaco which still, in theory, permit their monarch to withhold assent to laws, the monarch almost never does so, except in a dire political emergency or on advice of government. While the power to veto by withholding royal assent was once exercised often by European monarchs, such an occurrence has been very rare since the eighteenth century.

The Scottish Militia Bill 1708 was a bill that was passed by the House of Commons and House of Lords of the Parliament of Great Britain in early 1708. However, on 11 March 1708, Queen Anne withheld royal assent on the advice of her ministers for fear that the proposed militia would be disloyal. This was due to the sudden appearance of a Franco-Jacobite invasion fleet en route to Scotland which gave ministers second thoughts, at the last minute, about allowing it to reach the statute books. As of 2025, it is the last occasion on which the royal veto has been used in Great Britain or the United Kingdom.

A veto is a legal power to unilaterally stop an official action. In the most typical case, a president or monarch vetoes a bill to stop it from becoming law. In many countries, veto powers are established in the country's constitution. Veto powers are also found at other levels of government, such as in state, provincial or local government, and in international bodies.