The UK has fresh evidence of the use of chemical weapons on outskirts of Damascus, Britain\'s Prime Minister David Cameron has told the BBC. Scientists at the Porton Down laboratories have been \"examining samples\" from Syria\'s capital, he said, denying claims he had \"no hand to play\" over Syria after losing a vote last week on UK military action. He said the UK would lead calls for more action on aid for refugees and push for fresh peace talks. Cameron said he took \"full and personal responsibility\" for the decision to recall Parliament and could not have guaranteed MPs a say in whether Britain should take part in US-led action had he not acted so swiftly. His \"only regret\" was that Labour, which voted with Tory and Lib Dem rebels against the government motion, had chosen \"the easy and the political path not the right and the difficult path\". Asked if he had no hand to play at the Saint Petersburg summit, which is expected to be dominated by discussions about Syria, he said: \"Not in the slightest.\" Cameron added: \"Britain will be leading the argument on humanitarian aid. Britain will be one of the leaders in bringing forward plans for a peace process for Syria. Britain will be leading the argument across the globe for continuing to respond strongly on chemical weapons.\" He said: \"I absolutely believe that, having set a red line on the further big use of chemical weapons, it would be wrong if America was to step back and, having set that red line, to do nothing. I think that would send an appalling signal to President Assad and also to dictators elsewhere.\" The Damascus government is accused of using chemical weapons against civilians on several occasions during the 30-month conflict - most recently on a large scale in an attack on August 21 on the outskirts of the capital. The Syrian government has denied involvement and said the opposition was responsible. However, Cameron said evidence of the Assad regime\'s use of chemical weapons was \"growing all the time\" and scientists at the UK\'s chemical warfare research laboratories were investigating the attacks on 21 August 21. \"We have just been looking at some samples taken from Damascus in the Porton Down laboratory in Britain which further shows the use of chemical weapons in that Damascus suburb,\" he said.