Armed Conflict (Parliamentary Approval)

The Leader of the House is having difficulty answering the central question of when a vote would be triggered in the event of mission creep, but he is also having trouble with saying when the House, having held an initial vote, might be able to vote again if circumstances change. For example, let us suppose that the House votes to approve the deployment of forces in a war. If the main reason for going to war changes, should the House vote again?