The poisoning of a couple in Wiltshire was caused by the nerve agent Novichok, the same substance used against a former Russian spy and his daughter four months ago.
The couple, believed to be Charlie Rowley and Dawn Sturgess, are said to be in a critical condition. They were hospitalised after being found unwell on Saturday in Amesbury, just a few miles away from Salisbury where ex-double agent Sergei Skripal and his daughter Yulia were attacked in March.
Britain's Counter Terrorism Policing Network is now leading the investigation.
Metropolitan Police Assistant Commissioner Neil Basu spoke to reporters:
"Following the detailed analysis of those samples, we can confirm that the man and woman have been exposed to the nerve agent Novichok, which has been identified as the same nerve agent that contaminated both Yulia and Sergei Skripal. However, we are not in a position to say whether the nerve agent was from the same batch that the Skripals were exposed to."
The March attack prompted the biggest Western expulsion of Russian diplomats since the Cold War. Allies in Europe and the United States sided with Prime Minister Theresa May's view that Moscow was either responsible or had lost control of the nerve agent.