A Downing Street spokesperson said:

We have always made clear that we want the UN Security Council to live up to its responsibilities on Syria. Today we are giving its permanent members the opportunity to do that.

Britain has drafted a resolution condemning the attack by the Assad regime, and authorising all necessary measures under Chapter 7 of the UN Charter to protect civilians from chemical weapons.

The resolution will be put forward at a meeting of the 5 permanent members of the Security Council later today in New York.