Inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW) have begun work at the scene of the nerve agent attack on former Russian agent Sergei Skripal in the English city of Salisbury, a Reuters photographer said.

The inspectors were seen arriving at the Mill pub in Salisbury where Skripal and his daughter Yulia had a drink on March 4.

The pair were later found unconscious on a bench outside The Maltings shopping centre. They remain critically ill in hospital.