David Cameron will set out the case for British jets and drones to strike at Islamic State (IS) in Syria in an escalation of the UK's involvement in the war against the jihadist group.
The Prime Minister will tell MPs he believes there is a need to strike at the terrorists in their Syrian stronghold as well as in Iraq, where the RAF is already hitting IS targets with bombs and missiles.
Mr Cameron believes that action against IS in Syria is needed to strike at the "head of the snake" and thinks the RAF's highly-accurate Brimstone missiles offer a capability which its allies lack.
The Prime Minister has promised to set out a "comprehensive strategy" for dealing with IS in his response to a report by the Commons Foreign Affairs Committee (FAC), which raised a series of concerns about the prospect of further UK military intervention.
The atrocities in Paris have strengthened his resolve on the issue and a vote on air strikes could take place as soon as next week, although Mr Cameron has insisted he will not "bounce" MPs into a decision.
He has made clear that he will not seek a vote in the House of Commons on backing air strikes in Syria unless he is confident a majority of MPs will back him.
Labour's stance on the issue is unclear, with Jeremy Corbyn understood to have told colleagues that he wants to establish a collective position on the issue.
This could expose a deep rift, as while the leader has indicated he opposes military action against IS, a number of shadow ministers are likely to support it or choose to abstain.
The Prime Minister set out some of his thinking in the Commons yesterday when he told MPs that although air strikes on their own would not be enough it would be wrong to wait for political progress in Syria before targeting IS.
He said: "One of the lessons I would say we should learn from the last century is that when your country is under threat, and when you face aggression against your country, you cannot endlessly sit around and dream about a perfect world--you need to act in the world we are in."
At Prime Minister's Questions he said there was a "clear and present danger" from the group, which is also known as Isis, Isil or Daesh.
He said: "I am not for one minute arguing that action from the air alone can solve the very serious problem we have with Isil.
"Clearly we need a political settlement in Syria and a government in Syria that can act comprehensively with us against Isil."
But he challenged MPs to decide: "Can we afford to wait for that political settlement before we act? And my view is no, we can't wait for that political settlement.
"We should work as hard as we can for it but we should be acting now with allies because it is about keeping our own people and our own country safe."
He added: "There is a clear and present danger to the United Kingdom from Isil, based in Iraq and Syria, planning attacks against our country today.
"We do not live in a perfect world and we cannot deliver a perfect strategy, but we can deliver a clear, long-term strategy that will work."
The massacre of civilians in Paris, progress in Syria peace talks in Vienna and a UN Security Council resolution calling on states to take "all necessary measures" to tackle IS have changed the position since the FAC's report.
The committee's Conservative chairman Crispin Blunt has indicated the conditions set in the report could now be met.