A police officer who helped at the scene is also seriously ill

British police believe a nerve agent was used to try to murder a former Russian double agent and his daughter in Salisbury.

Sergei and Yulia Skripal were found unresponsive on a bench in the Wiltshire city on Sunday.

Health bosses are stressing that the risk to the public is low.

The UK's head of counter terrorism Mark Rowley gave an update at Scotland Yard, and confirmed a police officer is also ill: "These two people remain critically ill in hospital. Sadly, in addition, a police officer who was one of the first to attend the scene and respond to the incident is now also seriously ill in hospital. Wiltshire Police are providing every support to his family."