What is Salisbury convention under English law?

The Salisbury Convention is a constitutional convention in the United Kingdom that relates to the relationship between the House of Commons and the House of Lords. Specifically, the convention applies to the passage of legislation that has been promised in the governing party's election manifesto. It is named after the Marquess of Salisbury, who was the Prime Minister of the UK from 1885 to 1902. The Salisbury Convention holds that the House of Lords will not vote against legislation that was promised in the election manifesto of the party that forms the government, or any legislation that implements that manifesto. This is based on the principle that the elected government has a mandate from the people to implement the policies that it has promised in its manifesto. The convention is not a legally binding rule, but rather a political convention. However, it has been followed by the House of Lords in most cases since it was first established in the 1940s. The Salisbury Convention does not apply to legislation that was not included in the governing party's election manifesto or to legislation that was not explicitly promised in the manifesto. The convention also does not apply to legislation that is introduced by the opposition or by members of the House of Lords.