article: He told an emergency debate that UK intelligence chiefs believed it "highly likely" the Syrian government was responsible for the 21 August attack. But he said MPs must make a judgement call ahead of a Commons vote. The UK could launch strikes without UN backing, according to legal advice. Action would be a legal "humanitarian intervention" - even if it was vetoed at the UN, the government's summary of the advice said. Mr Cameron told MPs - who have been recalled early from their summer recess - he was convinced it was "beyond doubt" Syrian President Bashar al-Assad's regime was behind the attack. By Nick RobinsonPolitical editor But he added: "In the end there is no 100% certainty about who is responsible." Mr Cameron also stressed that unless action was taken Damascus would conclude it could use such weapons again and again. UK opposition leader Ed Miliband said Labour was not ruling out military intervention but insisted there had to be a clear road-map to a decision. Meanwhile, the five permanent members of the UN Security Council met to discuss the crisis. Two of them, Russia and China, have blocked previous resolutions on the issue and analysts predict they will again. Russia - Syria's main international ally - called the meeting, which has now ended with no progress towards a consensus, the BBC understands. The Syrian government has denied it is behind the suspected chemical attack near Damascus last week, in which hundreds of people are reported to have died, blaming opposition forces. US President Barack Obama has said he has not yet decided on a plan for action against Syria, but the White House has said any response will be based on US national security interests. The White House is due to give senior US Congress members a classified briefing on why it is certain Syria has used chemical weapons. Other nations are also considering the next move. UN Secretary General Ban Ki-moon has called for patience and insists he will receive a report on Saturday from weapons inspectors investigating the attack. By Gordon CoreraSecurity correspondent, BBC News The shadow of Iraq still hangs over the use of intelligence to justify military action. More than a decade on, we are presented with a very different document. This time we get the conclusions and overall assessment but not the evidence that lies behind them. And so while the government will hope the overall conclusion that it is "highly likely" the regime was responsible, there will still be ammunition for sceptics. They will say they need to see the evidence and not just assessments and judgements. The language used is one of probability rather than certainty - that is partly the reality of intelligence assessment, but also suggests there is no single, conclusive piece of intelligence which sweeps away all doubt. It also raises other questions which are not answered. What was the trigger for such a large use of chemical weapons when inspectors were in the country? Was it the result of an order from the top or could it have been
summary: Prime Minister David Cameron has put his case for military action against Syria to British MPs, but has conceded intelligence that the regime used chemical weapons is not "100% certain".