Public Health England (PHE) has issued new advice to hundreds of diners and pub-goers in the wake of the Salisbury attack.
The guidelines apply to anyone who was at the places where Sergei and Yulia Skripal drank and ate in the hours before their collapse.
Last week the almost 500 people who had visited the pub and the restaurant concerned were told to wash clothes they were wearing and double bag items that require dry cleaning.
Now, 12 days later, the advice has been revised.
It came as the nearby Porton Down lab denied any link to the nerve agent used in the attack.
Gary Aitkenhead of the Defence Science & Technology Lab said: "We would not be allowed to operate if we had lack of control that could result in anything leaving the four walls of our facility here.
"So we have got complete confidence that there is nothing that could have come from here out into the wider world as it were."
Investigators earlier removed the bench where poisoned former Russian double-agent Skripal and his daughter were found.
The Metropolitan Police said the attempted murder probe is likely to take months and involves 250 counter-terror detectives.
Door handles and computer keyboards were also taken from the home of Mr Skripal's home as chemical weapons experts work to establish where and how the nerve agent attack on the Russian former spy took place.
Scotland Yard said the bench is being taken to "preserve it as a potential crime exhibit".
Mr Skripal, 66, and his 33-year-old daughter, Yulia, were extremely ill when they were discovered on the park bench in The Maltings shopping centre on March 4.
The bench, a short walk from Zizzi restaurant and The Mill pub, which were both visited by the Skripals, has been cordoned off and covered by a tent since the incident.
Officials used a saw to remove the bench from its foundations before taking it away.
The pair remain unconscious and in critical but stable conditions.
The chief constable of Wiltshire, Kier Pritchard, has said the investigation is complex with no clear end in sight.
He said: “The investigation is highly likely to take many months and where it is operationally possible, updates will be issued to the media. We thank the public for their continued support.”