Syria 'chemical attack' intelligence findings examined
5 September 2013 Last updated at 23:08 BST
David Cameron says Britain has fresh evidence of chemical weapons use in Syria, but what do tests carried out in the UK reveal and how does this compare to the findings of other nations?
The USA and France believe President Assad's forces were responsible for a recent attack near Damascus that left more than 1,400 people dead, but Russia disputes the credibility of much of the evidence.
Gordon Corera reports.