Prime Minister Theresa May said police and prosecutors now believe the attack on Sergei Skripal was carried out by two Russian military intelligence officers who were nearly certainly acting with the approval of senior Russian officials.
Skripal, a former colonel in Russian military intelligence who betrayed dozens of agents to Britain's MI6 foreign spy service, and his daughter Yulia, were found unconscious on a public bench in the southern city of Salisbury on March 4. A police officer, Nick Bailey, was also hurt in the attack.
Basu said Novichok was sprayed on the front door of Skripal's house in Salisbury, where the two men were sighted on CCTV nearby.
The pair survived the poisoning, and today Britain's Crown Prosecution Service (CPS) said ithad obtained a European arrest warrant for two men, Alexander Petrov and Ruslan Boshirov, over the attack.
The "operation (was) nearly certainly approved at senior levels of (the) Russian state", it said.
The case has been likened by British politicians to the murder of Russian dissident and former KGB spy Alexander Litvinenko, who was poisoned with a rare radioactive isotope in a London hotel in 2006. "London has numerous requests from the Russian side".
A RUSSIAN spy wanted for the attempted murder of Sergei Skripal reportedly had visited Britain nearly exactly one year before the Novichok attack in Salisbury.
The Kremlin rejected the claims that Mr Putin was responsible and said that it was not going to investigate the suspects. "I don't understand why this was done and what sort of signal the British side is sending".
In response to the incident, London in March expelled 23 Russian diplomats believed to be intelligence agents. The affair has worsened Russian relations with the West, already under strain over Ukraine, Syria and other issues.
"And now we have identified the individuals involved we can go even further", she said.
It is unlikely that the two men will ever face trial in the United Kingdom since Russia and the U.K.do not have an extradition treaty, and the Russian government continues to deny the credibility of the British investigation. Britain will update the U.N. Security Council at a meeting on Thursday.
Neil Basu, head of UK Counter Terrorism policing, said the plot was "a remarkably sophisticated attack" which appeared to be a clear assassination attempt.
Mrs May said 250 detectives had trawled through 11,000 hours of CCTV and taken more than 1400 statements to come to their conclusion.
Mr Fleming said the intelligence community had supported police in a "painstaking" and "highly complex" investigation into what happened after the poisoning of former Russian spy Sergei Skripal and his daughter Yulia in Salisbury on 4 March.
According to police, the suspects, both around 40 years old, flew to London from Moscow on March 2. They were both since discharged from the Salisbury District Hospital.
"The levels of Novichok we found in the room at the time of police sampling in May were such that they were not enough to cause short or long-term health effects to anyone exposed to it, at that point or thereafter", he said.
British prosecutors accuse Petrov and Boshirov of conspiracy to murder Skripal, attempted murder and the use of a banned chemical weapon. They are also charged with illegal use and possession of a chemical weapon.
The UK was not asking Moscow to extradite the men because Russian law forbids the extradition of its citizens, CPS Director of Legal Services Sue Hemming said in a statement on Wednesday.