The two remain in a critical condition in quarantine in a hospital.
One of the first responders, officer Nick Bailey, also fell ill after treating the victims. He was taken to intensive care, where currently he is in a serious but stable condition.
Another eighteen people, including members of the public, police officers, and emergency service workers, received treatment as a result of the nerve agent attack, reported Sky News.
“Multiple people have been treated, around 21 people, including the man and the woman found on the bench,” said acting chief constable of Wiltshire Police, Kier Pritchard.
“A number of those have been through the hospital treatment process, they are having blood-tests, support and advice.”
Pritchard said Skripal, Yulia, and Bailey are the only ones currently in hospital.
The attack is being treated as an attempted murder. However, critical details about the crime remain unclear, including who administered the poison, their motive, and how it was carried out.
Addressing lawmakers, Amber Rudd from British Home Secretary labelled the attack an “outrageous crime,” adding that the government “will act without hesitation as the facts become clearer.”
“The use of a nerve agent on UK soil is a brazen and reckless act. This was attempted murder in the most cruel and public way.” she said.
“The investigation now involves hundreds of officers following every possible lead to find those responsible.”
Russia has denied involvement in the attack.
According to the BBC, it may take weeks before the government can comment if there was any Russian involvement.
Nerve agents are a class of highly toxic chemicals that disrupt the messaging between the brain and the body. They stop the nervous system working and shut down bodily functions.
Skripal was granted refuge by the British in a Cold War-style spy swap at Vienna airport in 2010 . He was one of four prisoners Moscow agreed to release in exchange for 10 Russian spies arrested by the FBI, reported BBC.
Russia’s Federal Security Service (FSB) arrested Skripal in 2004 on suspicion of betraying dozens of Russian agents to the British MI6 foreign intelligence agency. He was sentenced to 13 years in prison in 2006 after a secret trial.