Her Majesty's Most Loyal Opposition, or the Official Opposition, in the United Kingdom is led by the Leader of the Opposition. This is usually the political party with the second-largest number of seats in the House of Commons, as the largest party will usually form Her Majesty's Government. Since May 2010, the Official Opposition has been the Labour Party, currently led by Jeremy Corbyn.
The phrase His Majesty's Opposition was coined in 1826, before the advent of the modern two-party system, when Parliament consisted more of interests, relationships and factions rather than the highly coherent political parties of today (although the Whigs and Tories were the two main parties). The phrase was originally coined in jest; in attacking Foreign Secretary, George Canning, in the House of Commons, John Hobhouse said jokingly, "It is said to be hard on His Majesty's Ministers to raise objections of this character but it is more hard on His Majesty's Opposition to compel them to take this course."
The phrase was widely welcomed and has been in use ever since.
Whilst most days in the House of Commons are set aside for government business, twenty days in each session are set aside for opposition debates. Of these days, seventeen are at the disposal of the Leader of the Opposition and three can be used by the leader of the smaller, or Tertiary, opposition party (for most recent history this has been the Liberal Democrats, though currently they have been replaced by the Scottish National Party).