The Kremlin has insisted it is not involved, and said any allegations are a plot to whip up anti-Russian sentiment. This year's World Cup competition being hosted by Russian Federation is likely to be a target for some kind of boycott, say officials.
Nerve agents are highly toxic chemicals that resist the functioning of the nervous system and can be fatal.
Police say their deaths are part of the investigation into the poisoning of Mr Skripal and his daughter Yulia, who were found slumped on a park bench in Salisbury on Sunday evening. He is said to be in very serious, but stable condition. Officials did not immediately explain how the others might have been exposed to the substance. The public should not be alarmed and the public health advice remains the same.
The spokesman added: 'The Prime Minister wishes to again send her personal thanks to the police and emergency services for their courage in responding to the attack, and thank the people of Salisbury for their help and support'.
British government critics worry it will be difficult, if not impossible, to establish "hard evidence" that the Kremlin was behind the first-ever nerve agent attack on British soil.
"This was attempted murder in the most cruel and public way", said Rudd, Britain's top police official.
Ms Rudd has refused to speculate on whether the Russian state might have been involved in the attack, saying the police investigation should be based on "facts, not rumour".
On Tuesday Labour MP Yvette Cooper asked the home secretary to review 14 other deaths that had not been treated as suspicious by United Kingdom police, but have reportedly been identified by U.S. intelligence sources as being connected to the Russian state.
'We are committed to doing all we can to bring the perpetrators to justice, whoever they are and wherever they may be. He was released in 2010 and was moved to U.K.as part of a 10-person spy swap. Later in 2006, he was tried, convicted of high treason and imprisoned for 13 years.
Meanwhile, Alexander Goldfarb - a Russian dissident who was a friend of Alexander Litvinenko - recalled that Britain had accused two Russians with intelligence connections (Andrei Lugovoi and Dmitri Kovtun) of carrying out the murder.
BRITAIN has multiple options for a response if Russian Federation is proven to be behind a nerve agent attack on a former double-agent this week, according to Russian Federation expert Mathieu Boulegue.
On his deathbed he accused Russian President Vladimir Putin of being behind his radiation poisoning.
"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".
But proving Russian government involvement is another matter.
Blair, who led the London force when Litvinenko was fatally poisoned, 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. A total of 21 people, including Skripal and his daughter, have been treated after the apparent poisoning.
We are going to have to wait and see [on whether Sergeant Bailey would make a full recovery] on that. "This is not serious, it is pure propaganda and whipping up hysteria", Lavrov said.