RAF war planes are gearing up to launch air strikes on Syria after David Cameron announced that he was ready to seek the green light from Parliament to attack Islamic State (IS) militants in their heartland.
It is thought the first bombing missions could take place before the end of the week if the Commons votes tomorrow in favour of extending the current action against IS in Iraq into neighbouring Syria.
The Prime Minister's decision to seek the support of the House came after Jeremy Corbyn was forced to give Labour MPs a free vote in the face of a threatened revolt during a stormy meeting of the shadow cabinet.
The climbdown was seen at Westminster as a crushing humiliation for the Labour leader – who was reportedly shouted at by shadow ministers - after he made clear at the weekend he would decide whether the party's MPs would be whipped or allowed to vote with consciences.
Returning to Downing Street after attending the opening of international climate change talks in Paris on Monday, Mr Cameron said there was "growing support" across Parliament to intervene against IS – also referred as Isil, Isis or Daesh – in Syria.
"It is in the national interest, it is the right thing to do, we will be acting with our allies, we will be careful and responsible as we do so, but in my view it s the right thing to do this to keep our country safe," he said.
Mr Cameron will formally seek the backing of senior colleagues for his strategy at today's meeting of the Cabinet in Downing Street.
The Prime Minister rejected a call by Mr Corbyn for a two-day Commons debate – which would have meant delaying the vote until next week – although he made clear he would allow extended time for discussion tomorrow.
Foreign Secretary Philip Hammond indicated that if MPs voted for air strikes, more war planes would be deployed to the region to supplement the RAF Tornado GR4s already attacking IS in Iraq.
Labour sources suggested that 43% of Labour MPs – almost 100 out of the party's tally of 231 – supported air strikes in Syria, although it was unclear how many will vote with the Government.
Nevertheless, Mr Cameron – who has always said he would only go back to Parliament if he was sure of winning – clearly now believes that he has the numbers in the bag to offset any Tory rebels still opposed to intervening.
On the Labour side there was widespread dismay at Mr Corbyn's handling of the issue, following his statement last week that he could not support air strikes – seen by critics as an attempt to pre-empt the shadow cabinet meeting.
Even before the Labour top team gathered at Westminster, Diane Abbott – one of Mr Corbyn's few shadow cabinet allies – was warning that it would be a mistake to give Labour MPs a free vote because it would hand victory to Mr Cameron "on a plate".
But with support for air strikes headed by shadow foreign secretary Hilary Benn and deputy leader Tom Watson – and even leadership loyalist John McDonnell calling for a free vote – Mr Corbyn had no choice but to back down.
Mr Corbyn will now open the debate for Labour while Mr Benn will wind-up – although they will speak on opposite sides of the argument.
A senior source acknowledged the arrangement was unusual but insisted that it was not "shambolic".
A spokesman for Mr Corbyn said Mr Cameron's refusal to allow a two-day debate showed his case for war was "falling apart".
"Matters of national security are far too important to be bulldozed through the House of Commons for political convenience," the spokesman said.