British police scrambled on Thursday to determine how a couple were exposed to the same nerve agent used on a former Russian spy earlier this year, leaving them critically ill.

The couple were taken ill on Saturday in the village of Amesbury, close to the city of Salisbury, where former double agent Sergei Skripal and his daughter Yulia were found slumped on a bench on March 4 in an incident that sparked a diplomatic crisis with Russia. The home secretary has accused Russia of using Britain as a "dumping ground for poison" after a second incident involving the nerve agent Novichok. Sajid Javid said the agent was the same as that used on ex-Russian spy Sergei Skripal and his daughter in March.