Prime Minister David Cameron, seeking parliamentary support for British involvement in airstrikes against Islamic State militants in Iraq, told lawmakers they should be prepared for a long fight.

“This will be a mission that will not just take months but years, and I think we have to be prepared for that commitment,” Cameron said in answer to a hostile question from an opposition Labour Party lawmaker. He told Parliament the threat of Islamic State, also known as ISIL, “is not fantasy, it’s happening in front of us and we need to face up to it.”

Cameron announced two days ago he was recalling Parliament to seek authorization for airstrikes. He said today that while he supported U.S.-led action against ISIL in Syria, he wasn’t proposing British participation there because there was no consensus for it.