The Conservative Party (officially the Conservative and Unionist Party) is the second largest political party in the United Kingdom in terms of sitting Members of Parliament (MPs), the largest in terms of public membership, and the oldest political party in the United Kingdom. It is arguably the oldest organised political party in the world in that it can trace its evolution from early Tory parliamentary groupings of the eighteenth century; its only rival for seniority among the world's political parties is the Democratic Party of the United States, which also traces its direct roots to the 18th century. It is also the most successful political party in British history in terms of election victories. The current leader is David Cameron, who as Her Majesty's Loyal Leader of the Opposition heads the Shadow Cabinet.
The Conservative Party is descended from the Tory Party of the eighteenth and nineteenth Centuries. Its members are still commonly referred to as Tories and the party is still often referred to as the Tory Party. Although the Conservative Party was in government for two-thirds of the twentieth century, it has been in opposition in Parliament since losing the 1997 election to the Labour Party under Tony Blair.