Jeremy Corbyn has questioned whether British airstrikes in Syria would make Britain safer from ISIL - despite being told that UK intelligence shows ‘the risks of inaction’ are greater.
David Cameron told a sombre House of Commons that the head of MI5 and the Joint Intelligence Committee (JIC) had come to a clear verdict that the threat posed by the Islamist terrorists was so great that military action was now needed.
As he published a seven-point plan for Syria, he conceded that Britain’s military involvement could last ‘many years’ but declared that “my first responsibility as Prime Minister - and of this House - is to keep the British people safe”.
“We have to ask ourselves whether the risks of inaction are greater than the risk of taking action...all of the advice I've received says..the risk of inaction are greater".
Stressing he had learned the lessons of the Iraq war intelligence failures, he revealed that MI5's chief Andrew Parker and the JIC had assessed that the UK was now 'in the top tier of countries ISIL was targeting'.
And in the wake of the Paris attacks, but also those in Tunisia and elsewhere, he said that the UK's allies "could be forgiven for asking if not now, when?"
Mr Cameron - who said ‘every word’ of his statement had been cleared by intelligence chiefs - for the first time unveiled a key claim that 70,000 Kurds and Syrian rebels could be used as ground troops in alliance with RAF and other forces in the fight against ISIL.
Pleading with MPs for a 'clear majority' for action, he insisted that there would be no UK ‘boots on the ground’ and pledged £1bn in reconstruction costs for Syria.
However, Mr Corbyn made clear he remained unconvinced by either Mr Cameron or by the private briefing on security and the ISIL threat given to him by senior intelligence chiefs on Wednesday night.
The Labour leader, who is under pressure from his Shadow Cabinet to back military action and to allow a free vote when the issue is decided next week, set out his own worries.
“The question must now be whether extending the UK bombing from Iraq to Syria is likely to reduce, or increase, that threat and whether it will counter, or spread, the terror campaign ISIS is waging in the Middle East,” he said.
Mr Corbyn pointed to the “relatively marginal and remote Free Syrian Army” and suggested it was “more likely that other stronger jihadist and radical Salafist forces would take over” if ISIL was defeated.
“Without credible or acceptable ground forces, isn’t the logic of an intensified air campaign mission creep and western boots on the ground?,” he asked.
In a series of questions that made plain his own deep reservations, he demanded to know if the UN resolution passed last week offered “clear and unambiguous authorisation” for UK air strikes.
Mr Corbyn said that the central question was whether “UK bombing of Syria could risk more of what President Obama called ‘unintended consequences’”.
He concluded with a suggestion that “lasting defeat of ISIS can only be secured by Syrians and forces from within the region”.
Labour’s Shadow Cabinet meets later today to discuss the Cameron plan and will make a final decision on its policy on Monday.
With a majority of just 12, the Government needs Labour support to win any vote authorising the RAF to join other nations in the bombing of ISIL in its stronghold of Raqqa in north east Syria.
The SNP’s Angus Robertson today announced that his party would not vote for the action unless Mr Cameron could answer questions on the viability of ground forces and reconstruction costs.
Many MPS expect a vote on Syria next week, but Mr Cameron warned that he would not go ahead without proper cross-party support because a Commons defeat would be a 'publicity coup for ISIL'.
"There will not be vote in this House unless there is a clear majority in favour of action," he said.
Mr Cameron admitted that “the true arrival of ground forces awaits a new Govt in Syria” but said that the West had to work with President Assad in the meantime and that ‘Swiss-style democracy’ would have to wait until the terror threat was degraded.
He stressed that his was an "ISIL-first strategy", which wanted to weaken the terrorists first and then put in place a new government in Syria.
The PM admitted that the recent shooting by Turkey of a Russian jet had complicated the bid to get a united front, but said 'the gap' between himself and Vladimir Putin was narrowing on the long-term solution for Syria.
Many Tory MPs and some Labour MPs got up to give their backing to Mr Cameron, including previously sceptical figures such as Crispin Blunt - whose Foreign Affairs Committee had warned that UK air strikes would have ‘marginal effect’ unless other key diplomatic, military and legal tests were passed.
However, a handful of Tory MPs made clear they remain unpersuaded, including John Baron, Peter Lilley and Sir Edward Leigh,
Julian Lewis, chairman of the Defence Select Committee, said the figure of 70,000 Syrian ground troops was ‘a revelation to me’, while others pointed out the Free Syrian Army was fighting Assad not ISIL.
But former Defence Secretary Liam Fox told the Commons that on the threat posed by ISIL: “The question is whether we confront them over there - or whether we confront them over here"
The Prime Minister's official spokeswoman said senior Labour, Lib Dem, SNP and DUP figures had been briefed by the Government's national security adviser.
She said Mr Cameron suggesting MPs should consider the report "over the weekend" did not signal a vote would definitely take place next week.
She said: "We are not setting a time-table. People need time to reflect on the arguments."
Questioned about what a "clear majority" represented, she said "those will be judgements to be made" and would not be drawn on whether the figure would be informed by whether Mr Corbyn allowed his MPs a free vote.
On who the 70,000 fighters engaged in conflict with ISIS are, she said: "We look at their ideology and we look at their tactics ... based on a detailed analysis."