Traces of a nerve agent used in an attack on the Russian former spy Sergei Skripal and his daughter have reportedly been found in the Zizzi restaurant in Salisbury.
Hundreds of pub-goers and diners have been told to wash possessions as a precaution after nerve agent traces were found.
Interior minister Amber Rudd says the government is doing all it can to advance the investigation.
"The key thing is, as a government, we have made it clear that we will make sure that all the resources are put into this investigation to ensure that it can proceed at speed with all the resources necessary," she explains.
British police have identified more than 200 witnesses and are looking at more than 240 pieces of evidence.
After an emergency meeting of the country's Cobra security committee, Rudd said it was still "too early" to say with certainty who was behind the poisoning.
Meanwhile troops remain on the city's streets.
Police called in about 180 marines, soldiers and air force personnel with expertise in chemical weapons, decontamination and logistics to help with the probe and remove vehicles that might be contaminated.