Russian ex-spy Sergei Skripal and his daughter Yulia remain in hospital in a critical but stable condition after they were poisoned with a nerve agent, interior minister Amber Rudd says.
Nick Bailey, a police officer who fell ill after being part of the early response to the attack, remains seriously ill but is talking and engaging with his family, Rudd said on Saturday after chairing a meeting of the government's Cobra security committee.
Skripal, 66, and Yulia, 33, were found unconscious on a bench on Sunday in the southern English city of Salisbury.
British police have identified more than 200 witnesses and are looking at more than 240 pieces of evidence in their investigation, Rudd said.
Rudd told reporters that more than 250 counter terrorism police were involved in the investigation, which was proceeding with "speed and professionalism".