The Salisbury Convention (officially called the Salisbury Doctrine, the Salisbury-Addison Convention or the Salisbury/Addison Convention) is a constitutional convention in the United Kingdom under which the House of Lords will not oppose the second or third reading of any government legislation promised in its election manifesto.
Following a landslide Labour general election victory in 1945, there were only 16 Labour peers in the House of Lords, led by Lord Addison. Throughout the 20th century, the second chamber had an in-built Conservative majority. However, because Clement Attlee's Labour government had a clear electoral mandate to deliver the policies of nationalisation and welfare state measures, it was generally felt that the unelected House of Lords should not oppose such legislation at second reading.
Lord Addison and Lord Salisbury (then Lord Cranborne), the Conservative leader in the House of Lords from 1942 to 1957, both with memories of the troubles leading to the passing of the Parliament Act 1911, agreed that anything promised in a party's manifesto would eventually pass but that anything else would be subject to full debate. In its modern form, the convention still permits the offering of reasoned amendments to a motion for second reading of a Government bill, provided such amendments are not wrecking amendments designed to destroy the bill.
After the Labour general election victory in 2005, the Liberal Democrats indicated that they did not feel bound by the Salisbury Convention as a result of decreasing voter turnout, the low share of the vote received by the Government, and the changes to the composition of the House of Lords introduced in 1999 by the Labour Government.
In 2006, Tony Blair appointed Lord Cunningham of Felling to chair a joint committee of both Houses of Parliament to investigate possibilities of formalising numerous conventions including the Salisbury Convention.