The Salisbury convention had its roots in the theory developed in the late 19th century by the 3rd Marquess of Salisbury that the House of Lords was entitled to reject bills passed by the Commons unless the Commons could be considered to have a mandate from the country to enact the legislation in question. This theory, which was intended to preserve the declining power of the Lords, became a means of cementing the primacy of the Commons. The modern form of the doctrine was first formulated after the 1945 Labour landslide election victory by Viscount Cranborne, the leader of the Conservative opposition in the Lords:
Whatever our personal views, we should frankly recognise that these proposals were put before the country at the recent General Election and the people of this country, with full knowledge of these proposals, returned the Labour Party to power. The Government may, therefore, I think, fairly claim that they have a mandate to introduce these proposals. I believe it would be constitutionally wrong, when the country has so recently expressed its view, for this House to oppose proposals which have been definitely put before the electorate.This doctrine was expressly limited to measures which had been in the Labour Party's manifesto at the preceding election. Cranborne was the grandson of the 3rd Marquess of Salisbury (and succeeded to the title in 1947), hence the name given to the convention. It is sometimes known in political circles as the 'Salisbury-Addison' convention, Viscount Addison being the Leader of the Lords in the Attlee government.
The convention was observed by the Lords between 1945 and the mid-1990s, when the continuing validity of the doctrine began to be questioned. The issue became a live one in 1997, when a Labour government was elected on an express mandate of reforming the House of Lords, a policy that came to fruition in the House of Lords Act 1999. Could a doctrine that arose out of an understanding between two senior Labour and Conservative politicians at a time when the Lords had a permanent hereditary Conservative majority be considered to be binding on all parties in an era when the great majority of the hereditary peers had been evicted and no party had an overall majority in the Lords? Was it not artificial to presume that voters read party election manifestoes, or did so in detail? The 1945 Labour manifesto had run to only 8 pages, whereas the 2010 version was 78 pages long.
The leader of the Conservative opposition in the Lords, Lord Strathclyde, publicly questioned the future of the convention in a 1999 lecture to the think-tank Politeia and in a parliamentary debate in 2001. However, his Labour counterpart Baroness Jay reaffirmed the validity of the convention in a reply to a parliamentary question on 15 December 1999. Further doubts about the convention were raised in 2000 by the Wakeham commission on the future of the Lords, though its underlying principles were reaffirmed.
In 2006, a parliamentary Joint Committee on Conventions produced a report that dealt with the Salisbury convention. The Conservatives and Labour both supported the convention. The Lib Dems were considerably cooler about it, though in fact they took the position that the Lords should not reject government bills at all. Two constitutional experts, Rodney Brazier and Anthony Bradley, thought that the convention had either passed into history or was in need of reformulation.
Halsbury's Laws sums up the doctrine in this way:
By the 'Salisbury' doctrine it is unconstitutional for the Lords to refuse their consent to legislation that seeks to give effect to a manifesto commitment of the governing party.A House of Lords library note dating from June 2006 states:
The Salisbury doctrine, as generally understood today, means that the House of Lords should not reject at second or third reading Government Bills brought from the House of Commons for which the Government has a mandate from the nation.The Joint Committee on Conventions produced the following, more detailed definition in November 2006:
98. The Convention now differs from the original Salisbury-Addison Convention in two important respects. It applies to a manifesto Bill introduced in the House of Lords as well as one introduced in the House of Commons. It is now recognised by the whole House, unlike the original Salisbury-Addison Convention which existed only between two parties.
99. The Convention which has evolved is that:
In the House of Lords:
A manifesto Bill is accorded a Second Reading;
A manifesto Bill is not subject to 'wrecking amendments' which change the Government's manifesto intention as proposed in the Bill; and
A manifesto Bill is passed and sent (or returned) to the House of Commons, so that they have the opportunity, in reasonable time, to consider the Bill or any amendments the Lords may wish to propose.
100. In addition the evidence points to the emergence in recent years of a practice that the House of Lords will usually give a Second Reading to any government Bill, whether based on the manifesto or not. We offer no definition of situations in which an attempt to reject a Bill at Second Reading might be appropriate, save that they would include free votes. But to reject Bills at Second Reading on a regular basis would be inconsistent with the Lords' role as the revising chamber. In practice the Lords have the means to express their views on the principles of a Bill without rejecting it at Second Reading, by tabling a non-fatal motion or amendment at Second Reading.