The Prime Minister has said parliament should only have a vote on military action ahead of a long-planned war, during the second day of debate about the allied airstrikes in Syria last Friday.
Responding to a motion proposed by Labour leader Jeremy Corbyn, she said it was right for MPs to be consulted on action, but outlined why it would have been wrong for her to recall parliament ahead of the action taken in response to the chemical attacks in Douma. She claimed any debate might have helped the enemy by alerting them to where and when British military would be.
"I had come here to this House to make the case for action in advance, I could not have concealed our plans and retained that uncertainty," she told MPs. "I would quite understandably have faced questions about the legality of our action. The only way I could have reassured the House would have been to set out in advance, as I did yesterday after the event, the limited, targeted and proportionate nature of our proposed action."
May added: "I would have faced questions about what aircraft and weapons we were planning to use, when the operation was going to take place, how long it was going to last and what we were going to do. All of this would have provided invaluable information that would have put our armed forces at greater risk and greatly increased the likelihood of the regime being able to shoot down our missiles and get their chemical weapons away from our targets. I was not prepared to compromise their safety and the efficacy of the mission.
The Prime Minister claimed Corbyn's plan for a War Powers act was unpractical because "it would mean many smaller scale, timely and targeted interventions, like the action we have taken to alleviate further humanitarian suffering by degrading Syria’s chemical weapons capability and deterring their use, would become unviable - unviable because it would significantly reduce the effectiveness of any operations and endanger the safety of our servicemen and women".
However on a full scale deployment, such as the Iraq War, where plans are built over a longer period "it is absolutely right and appropriate for parliament to debate military action in advance", she said. "But that does not mean it is always appropriate. It therefore cannot and should not be codified into parliamentary right to debate every possible overseas mission in advance."
She claimed a War Powers Act would remove the Prime Minister's ability to act with intelligence that cannot be shared and debated more widely.
Corbyn's motion, that MPs had "considered Parliament's rights in relation to the approval of military action by British Forces" was passed by 317-256, even though Labour MPs had been whipped to vote against it.