The U.K.’s head of Counter Terrorism Policing Neil Basu (right) and the chief medical officer for England Dame Sally Davies, speak at a news conference at New Scotland Yard in London on Wednesday. British police say a couple who are critically ill were exposed to the Russian nerve agent Novichok.

The U.K.’s head of Counter Terrorism Policing Neil Basu (right) and the chief medical officer for England Dame Sally Davies, speak at a news conference at New Scotland Yard in London on Wednesday. British police say a couple who are critically ill were exposed to the Russian nerve agent Novichok.