Jeremy Corbyn has set the stage for a showdown with his own shadow cabinet after insisting that he alone has the final decision on whether Labour opposes air strikes in Syria.
The leader again refused to commit to offering a free vote to his MPs as he delivered an impassioned critique of David Cameron's case for attacking Islamic State in its heartlands.
He also insisted politicians must listen to the "voice" of the party membership, which overwhelmingly elected him.
The intervention, in an interview on the BBC's Andrew Marr show, is likely to inflame tensions further between Mr Corbyn and his top team amid open warnings of resignations.
The shadow cabinet is due to meet tomorrow to try to hammer out a collective position ahead of a potentially explosive gathering of the parliamentary party in the evening.
In a defiant performance, Mr Corbyn dismissed intelligence advice that IS was using its territory in Syria to prepare terror atrocities against Britain, arguing that "those attacks could be planned anywhere".
He also "seriously questioned" the Prime Minister's claim that there are 70,000 moderate Syrian troops to tackle IS forces on the ground, and voiced doubts about their "loyalties".
Mr Corbyn said a unanimously-passed UN Security Council resolution calling for "all necessary measures" against the terrorist groups did not provide justification for military action.
Bombing IS targets in Syria would be a "distraction from the political process" to end the civil war, and would lead to civilian casualties.
Asked whether Labour MPs - dozens of whom are thought to be considering supporting action - would be given a free vote, Mr Corbyn said: "No decision has been made on that yet, I am going to find out what MPs think.
"Obviously there are strong views on both directions. We will have a further discussion on this. We will make that decision not at this moment but later on."
Mr Corbyn said he had received 70,000 responses to a survey sent out to Labour supporters on Friday canvassing their opinions, and a decision would be taken "as a party". The poll has been criticised as an attempt to use his grassroots powerbase to "bounce" the shadow cabinet into submitting.
"My view about the membership of the Labour Party, they must have a voice," he said.
"Labour MPs need to listen to that voice, they need to try and understand where people are coming from on this. We will come to a decision as a party."
The veteran left-winger, who has been a serial rebel through his Commons career, said: "I understand dissent, I understand disagreement from leadership."
But asked if the whipping position would be a collective decision by the shadow cabinet, Mr Corbyn said: "It is the leader who decides. I will make up my mind in due course."
Asked if there was any chance divisions in the party could force his resignation, Mr Corbyn said: "I'm not going anywhere. I am enjoying every moment of it."
Defence Secretary Michael Fallon said he had been briefing Labour MPs on military action over the weekend but stressed the Government does "not yet" have a guaranteed majority to back airstrikes.
The Defence Secretary rejected claims that bombing Raqqa and other IS-held cities could lead to a large number of civilian casualties as the terror group retreats into tunnels or uses the local population as "human shields".
He claimed the RAF's precision airstrikes had not claimed a single civilian life during action taken against IS in Iraq, and that Britain had "very strict rules of engagement", and warned that the UK's reputation would be damaged and the population less safe if action was not taken in Syria.
Pressed on the nature of the 70,000-strong force in Syria Mr Cameron referred to, Mr Fallon said: "We do know who they are and this is an independent joint intelligence committee assessment, it's not ministers making this figure, it's their assessment and it's supported by academics."
Shadow chancellor John McDonnell told Pienaar's Politics on BBC Radio 5 Live that Mr Corbyn would take a decision on which way to whip in the morning, and make a recommendation to the shadow cabinet meeting.
"I want on these sort of issues an unwhipped vote, because they are above party politics," he said. "I am hoping he's taking my view into account the same as other party members."
Shadow justice secretary Lord Falconer confirmed there were "significant differences" within the shadow cabinet, and he did not think it would be possible to reach a collective view.
"It is unlikely that we will be able to agree a yes or no answer to the question the Government is about to propose," he told the BBC's Sunday Politics.
"My own view is I don't think this very very important issue should be a situation that forces resignations on people. I think the right course is if the shadow cabinet cannot come to a collective view - and I accept that may well be unlikely - probably the best course is a free vote."
Asked if he personally was ready to resign, Lord Falconer said: "I don't want to comment on that."
Deputy Labour leader Tom Watson also joined calls for a free vote - and suggested he could force a show of hands in the shadow cabinet on the issue if Mr Corbyn refuses to grant one.
"After the week that we've had, the best way of holding the party together, but allowing MPs to solemnly express what they feel, is for us to have a free vote," he told the Independent on Sunday.
Labour MPs Jess Phillips and Liam Byrne both signalled they could vote against airstrikes and called for the vote to be whipped, but criticised Mr Corbyn's handling of the situation.
Ms Phillips told BBC Radio 4's The World This Weekend: "If the Labour Party as a collective group of people cannot have a consensus position on this, that is very, very lamentable.
"I think it's been handled appallingly."
Mr Byrne said of the Labour leader: "I don't think that writing letters that prejudge the outcome, the conclusion of the shadow cabinet position, was a good way of approaching this."