Defence Secretary Philip Hammond has said that anyone found to be responsible for an alleged chemical attack in Damascus "should be in doubt that they will be held to account".
He said Britain is pushing with the "utmost urgency" for UN inspectors to be given access to the sites to make an "objective assessment".
Britain has directly accused the Assad regime of gassing hundreds of Syrian civilians amid warnings only 48 hours remain to find proof.
New videos show the eyewitness accounts of four men who witnessed an alleged chemical attack on Zamalka, a suburb of Damascus.
These are the images of the remains of rockets which, according to the men stood by them, delivered poisonous gas to a suburb of Damascus.