What year did XXX start?
Lascelles Principles
The Lascelles Principles was a constitutional convention in the United Kingdom between 1950 and 2011, under which the Sovereign could refuse a request from the Prime Minister to dissolve Parliament if three conditions are met: if the existing Parliament was still ``vital, viable, and capable of doing its job'', if a General Election would be ``detrimental to the national economy'' (and), if the Sovereign could ``rely on finding another prime minister who could govern for a reasonable period with a working majority in the House of Commons.''
1950