Up to 500 Salisbury pub-goers and diners have been told to wash possessions as a precaution after nerve agent traces were found.
Trace amounts of the substance used to poison ex-Russian spy Sergei Skripal and his daughter were found on and around a table where the pair ate at Zizzi restaurant, the BBC has learned.
The table, along with other items, has been removed and destroyed.
Scientists have advised police it could take weeks for the premises to reopen.
Traces of the nerve agent were also found at the Mill pub in Salisbury.
Sergei and Yulia Skripal, who remain in a critical but stable condition in hospital, are understood to have eaten on a table away from other diners.