Prime Minister David Cameron recalled Parliament today and made a case for the UK to join US-led air strikes against Islamic State (IS) terror network in Iraq which he warned could "not just take months but years".
Cameron told MPs that IS poses a "clear and proven" threat to British lives and was a "brutal", well-funded "terrorist organisation" that had destabilised Iraq and Syria.
"This is going to be a mission that will take not just months but years but I believe we have to be prepared for that commitment," he said while answering a question on the length and scope of the mission.
IS has seized large parts of Iraq and Syria in recent months.
The group, also known as ISIS or ISIL, has used tactics that have included beheadings of soldiers, Western journalists and aid workers.
It could have as many as 31,000 fighters in Iraq and Syria, according to the CIA.
British aid worker David Haines was beheaded by the terror group. Haines, 44, was seized in Syria in 2013 and was being held by IS militants who have already killed two US journalists.
All three main political parties in the UK - the Conservatives, Liberal Democrats and Labour -back UK military participation in bombings against IS in Iraq, which the coalition says is legal because it was requested by the Iraqi government.
Opening the Commons debate, Cameron said the threat posed by IS was not "on the far side of the world", saying it had already been responsible for one major attack in Europe and a number of other plots had been foiled.
"This is not the stuff of fantasy. It is happening in front of us and we need to face up to it," he said.
IS, he said, had "already declared war on us and there was no walk on-by option".
"It is our duty to take part. It is about protecting people on the streets of Britain," he added.
The government does not have to seek the approval of MPs to commence military action, but it has become customary to do so since this first happened over the Iraq war in 2003.
About 179 British personnel died in Iraq between 2003 and 2009 and the last British troops left the country only in 2011. Around 500 Britons are believed to have travelled to fight with IS.
Parliament is due to vote on UK involvement at the end of a seven-hour debate in the House of Commons later this evening. If the vote is passed, the UK would join the US and France in launching targeted strikes on the IS group in Iraq.
