The park bench where the former Russian spy Sergei Skripal and his daughter, Yulia, fell critically ill after a nerve agent attack has been removed and will be preserved as a potential crime exhibit.
Officers in protective clothing wrapped the bench in plastic before using an angle grinder and crowbar to cut it free and take it away in a white van.
In a statement, Scotland Yard said: “It [the bench] is being removed … in order to preserve it as a potential crime exhibit as part of the investigation into the attempted murders.”
It said that areas searched so far as part of the investigation included open spaces, commercial and residential properties and vehicles.
A spokesperson said: “This is one of the largest and most complex investigations undertaken by British counter-terrorism policing.
“Searches are ongoing in the Salisbury area and at this stage it is not possible to put a timescale on how long these may take to conclude. Specialist search officers wearing protective equipment continue to carry out a meticulous, systematic search for evidence to support the investigation.
What is novichok?
Novichok refers to a group of nerve agents that were developed by the Soviet Union in the 1970s and 1980s to elude international restrictions on chemical weapons. Like other nerve agents, they are organophosphate compounds, but the chemicals used to make them, and their final structures are considered classified in the UK, the US and other countries. By making the agents in secret, from unfamiliar chemicals, the Soviet Union aimed to manufacture the substances without being impeded.
“Much less is known about the novichoks than the other nerve agents,” said Alastair Hay, an environmental toxicologist at the University of Leeds who investigated the use of chemical weapons against Iraqi Kurds in Halabja in 1988. “They are not widely used at all.”
The most potent of the novichok substances are considered to be more lethal than VX, the most deadly of the familiar nerve agents, which include sarin, tabun and soman.
And while the novichok agents work in a similar way, by massively over-stimulating muscles and glands, one chemical weapons expert told the Guardian that the agents do not degrade fast in the environment and have “an additional toxicity”. “That extra toxicity is not well understood, so I understand why people were asked to wash their clothes, even if it was present only in traces,” he said. Treatment for novichok exposure would be the same as for other nerve agents, namely with atropine, diazepam and potentially drugs called oximes.
The chemical structures of novichok agents were made public in 2008 by Vil Mirzayanov, a former Russian scientist living in the US, but the structures have never been publicly confirmed. It is thought that they can be made in different forms, including a dust aerosol that would be easy to disperse.
The novichoks are known as binary agents because they become lethal only after mixing two otherwise harmless components. According to Mirzayanov, they are 10 to 100 times more toxic than the conventional nerve agents.
The fact that so little is known about them may explain why Porton Down scientists took several days to identify the compound used in the attack against Sergei and Yulia Skripal. While laboratories around the world that are used to police chemical weapons incidents have databases of nerve agents, few outside Russia are believed to have full details of the novichok compounds and the chemicals needed to make them.
“That search is being carried out based on expert scientific advice to assist detectives in understanding the specific locations that are of most relevance to their lines of inquiry.
“Around 250 counter-terrorism detectives continue to work round the clock, supported by a full range of experts and partners.”
The bench, close to the Mill pub and Zizzi restaurant, which the Skripals visited on 4 March before collapsing, has been cordoned off and protected with a tent.
Meanwhile, the chief executive of the defence laboratory at Porton Down said there was “no way” the site could be linked to the poisoning of the Skripals.
Gary Aitkenhead told the BBC that Russian claims that the proximity of the lab to Salisbury might be somehow suspicious were “frustrating” and insisted Porton Down had the “highest levels” of controls and security.
The environment secretary, Michael Gove, visited Salisbury on Friday. He acknowledged that businesses had taken “a bit of a hit” but said a plan was being developed to mitigate the problems the city faces.
Parking in some Salisbury car parks will be made free from Saturday to try to encourage visitors to return.
It also emerged on Friday that door handles and computer keyboards were among the items at Skripal’s home that are being examined by investigators as they work to establish where and how the nerve agent attack took place.
Skripal’s red-brick house in Salisbury remains cordoned off almost three weeks after the 66-year-old and his daughter, Yulia, 33, collapsed in the city centre.
An investigator was seen at the house with a list headed “swabs”. It appeared to indicate that the spots the Skripals were likely to have touched were being looked at in particular. The front door, patio door and keyboards were all listed.
Counter-terrorism officials have given no details of how the Skripals may have come into contact with the nerve agent, which has been identified as novichok.
There was speculation it could have been placed on the door handles of Skripal’s BMW or in the car’s ventilation system. Another suggestion is that Yulia, who arrived in the UK on a flight from Russia the day before she and her father collapsed, may have brought it into the country.