Police have placed a road in Salisbury on lockdown after a man fell ill outside Zizzis restaurant where the Skripals dined before their Novichok poisoning.
Police arrived on the scene on Castle Street just before 7pm this evening as they responded to an incident involving a man in his 30s.
Members of the public took to Twitter to describe the scene and shared images of numerous emergency vehicles on the street and officers wearing hazmat suits.
Despite the huge police and ambulance presence, it was later confirmed that there were no concerns for the man's health.
One onlooker wrote: "Major activity in #Salisbury. Police and search and rescue running into the railway station. Sirens audible for ages. Road shut in city centre, tent being erected here."
Another said: "Looks like the men in green suits are responding to a person outside Tesco’s in the Salisbury city centre next to zizzi’s restaurant a lot of shouting, Screaming at the individual on the floor."
A third added: "Castle Street in Salisbury closed off by emergency services, by Zizzi/Tesco..."
Wiltshire Police said: "Wiltshire Police says emergency services are attending an incident involving a man in his thirties at the Zizzi restaurant in Salisbury where Sergei and Yulia Skripal attended before becoming seriously ill in March."
Salisbury Police tweeted a statement which read: We are currently dealing with an incident in Castle Street, #Salisbury, involving a man in his 30s.
"Given the ongoing incident in Salisbury and Amesbury, we are taking highly precautionary measures to ensure public safety.We do not want people to be alarmed, but hope you understand the reasons behind this.
"We will update you when we have any further information.
"At the moment there is nothing to suggest any wider risk to the public. Please avoid the immediate area & be respectful of the cordon."
They later added: "He has been taken to Salisbury District Hospital and fully assessed by medical staff. We can now confirm that there is no concern for either his health or any wider risk to the public.
"We understand that our initial response to the incident may have looked alarming, but we hope you appreciate why we needed to take this highly precautionary measure. We thank you all for your patience and understanding."
Salisbury District Hospital later said in a statement that the man tested negative for Novichok.
An eyewitness who asked not to be named told the Press Association the man involved in the incident was a "local homeless guy" who was "sat on the floor, completely conscious, talking".
He said he saw a paramedic at the scene climbing into a chemical suit while another "was shouting at the man to stay put and stay on the floor".
"All the police officers had rubber gloves on, he added.
The man said that when he cycled past a second time there was a "small cordon with a handful of police and paramedics".
"Whilst cycling out of the city all the response vehicles descending on the city," he said.
Former Russian spy Sergei Skripal and his daughter Yulia were poisoned with the deadly chemical weapon on March 4 this year.
On June 30, a couple in Amesbury Dawn Sturgess and Charlie Rowley fell ill with symptoms of Novichok poisoning.
One of the lines of inquiry is that the couple came in contact with a phial or container used to transport Novichok for the Skripals poisoning.
Ms Sturgess died as a result of exposure to the deadly substance on July 7 while Mr Rowley is no longer in a critical condition.
Experts at Salisbury District Hospital said there has been a significant improvement in Mr Rowley's condition overnight, and he has now spoken to detectives.
A counter-terrorism chief this morning said he could not give any assurances that there are no more traces of the substance in the county, and said the heatwave had added to the challenges faced by investigators.
Assistant Commissioner Neil Basu, the national lead for counter terrorism said: "I would love to be able to stand here and say how we have identified and caught those responsible and how we are absolutely certain there are no traces of nerve agent left anywhere in the county.
"The brutal reality, however, is that I cannot offer you any such assurances or guarantees at this time."
He said scientists at the Defence, Science and Technology Laboratory at Porton Down are carrying out tests to establish whether the latest tragedy is linked to the poisoning of the Skripals.
Mr Basu said: "At this stage, we cannot say with certainty that both the incident in March and this latest incident are linked. Clearly, this is our main line of enquiry, but our investigation must be led by the evidence available and the facts alone.
"I would need a forensic link to be definitive, but this is a very rare substance banned by the international community and for there to be two separate distinct incidents in one, small English county is implausible to say the least."
Describing how Dawn and Mr Rowley came into contact with the substance, he said: "We believe that Dawn and Charlie handled some kind of container which the nerve agent was in, and we're focusing our efforts on finding this container."
But he warned the public not to expect fast results, stating: "Specialist officers are carrying out painstaking searches, but as I'm sure you will appreciate, this work is made all the more difficult as they have to carry out their activity in protective equipment, which significantly impacts the speed at which they can work.
"This, coupled with the extreme heat they have been working in, has proved extremely challenging for those carrying out this crucial work, but I know the officers are doing everything they possibly can to progress this as quickly as they can.
"However, we expect this work to take several weeks, if not months, but we simply cannot take any risks, both with our officers' safety, and with the safety of the public."
According to information given by scientists to Mr Basu, the nerve agent used in Salisbury could last for five decades.
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Salisbury police incident: Road closed after 'man falls ill near Zizzis where Skripals dined before poisoning'