The forensic tent, covering the bench where Sergei Skripal and his daughter Yulia were found, is repositioned by officials in protective suits in the centre of Salisbury, Britain, March 8, 2018.
On Thursday, the Home Secretary revealed a police officer who rushed to help is awake and talking in hospital.
Military personnel specialising in chemical and biological warfare have joined the investigation in Salisbury into the attempted murder of a former Russian spy and his daughter, who were allegedly exposed to a nerve agent by elements widely suspected to be of Russian origin.
Britain has said it will respond appropriately if evidence shows Russian Federation was behind the poisoning. Moscow has denied involvement and asserted that anti-Russian hysteria is being whipped up by the British media.
The news comes as a British police official has updated the number of people who sought treatment after the nerve agent attack, saying "around 21" had been given medical help and support.
Nerve agents are highly toxic chemicals that resist the functioning of the nervous system and can be fatal.
Ms Rudd said the pair are in a "very serious" condition five days after they were discovered slumped on a bench in Salisbury, Wiltshire.
Health chiefs have said there is a low risk to the wider public from the nerve agent used against the Skripals, who police said were deliberately targeted with the rare toxin.
Prime Minister Theresa May said her thoughts were with Det Sgt Bailey, adding: "The events of Sunday are a stark reminder, if ever one was needed, of the unsafe situations our emergency services face, and the dedication and courage they display every day in order to keep us safe".
"But if we are to be rigorous in this investigation, we must avoid speculation and allow the police to carry on their investigation".
British Prime Minister Theresa May said her government would respond appropriately if evidence showed Moscow was behind the attack on Mr Skripal, who served time in a Russian jail for spying for England, before he was released in a spy swap.
Putin praises Trump, says US system 'eating itself up'
Sergei Skripal and his daughter Yulia were found on a park in Salisbury, having come in to contact with a nerve agent. It was first awarded on Yom HaShoah of 1967 by then Prime Minister Levi Eshkol.
"We are committed to do all we can to bring the perpetrators to justice, whoever they are and wherever they may be", she said.
He was pardoned before being flown to Britain as part of a high-profile spy swap involving Russian Federation and the United States in 2010.
Russia's Federal Security Service (FSB) alleged he had begun working for MI6 while serving in the army in the 1990s.
Marina Litvinenko commented on the attack on former Russian secret service agent Sergey Skripal in an interview with CNN.
A British inquiry has concluded that the Russian government was behind Litvinenko's death and that President Vladimir Putin "probably approved" the killing.
"All of our staff that attended the incident in Salisbury in the Maltings, they performed the role that police officers and police staff do every day up and down the country".
However, he told Sky News: "Regardless of whether the Russians are involved in this case, they are fighting a new Cold War against us and you need to wisen up to that fact".
He told the BBC it is important to find out "whether there is some pattern here". He also suggested that Britain could reconsider the participation of its officials in the soccer World Cup in Russian Federation this summer.
Skripal and his daughter were in Salisbury city center from around 1:30 p.m. on March 4.
We are going to have to wait and see [on whether Sergeant Bailey would make a full recovery] on that.
The Financial Times said on Friday citing security officials that Skripal continued to provide information to western intelligence agencies after arriving in the United Kingdom in 2010.