that power suggesting over two years ago, the russians were able to save the damascus regime from collapse. they deployed ground forces and russian air force and surface-to-air missiles to probl protect air space and called for a no-fly zone on the damascus regime. the regime is feeling pretty secure, but only with russian backing. that security, though, does allow a degree of russian pressure to be brought to bear. the humanitarian corridors we have seen before during the capture of aleppo. they are safety valves to get people out, but humanitarian window dressing for damascus and kremlin. >> sam kiley, thank you. the uk foreign secretary boris johnson said if there is evidence of chemical weapons used, the uk could play a role in air strikes against the syrian regime.