Two Russian military intelligence officers are accused of carrying out the Salisbury nerve agent attack.
Police and prosecutors announced they had enough evidence to charge the men named as Alexander Petrov and Ruslan Boshirov over the poisoning in March.
Theresa May told MPs investigations have concluded that the two suspects are members of the GRU, Russia’s military intelligence service.
In a statement that will deepen the diplomatic crisis between the two countries, the Prime Minister said: “The GRU is a highly-disciplined organisation with a well-established chain of command. So this was not a rogue operation.
“It was almost certainly also approved outside the GRU at a senior level of the Russian state.”
Former Russian spy Sergei Skripal and his daughter Yulia were left critically ill after being exposed to the military grade nerve agent Novichok.
Exactly six months after news of the poisoning broke, two alleged perpetrators were identified in a dramatic joint police and Crown Prosecution Service press conference.
Detectives believe it is likely the pair, thought to be aged around 40, travelled under aliases and that Petrov and Boshirov are not their real names.
Prosecutors will not be applying to Russia for the extradition of the two men, but a European Arrest Warrant has been obtained.
Detectives believe the front door of Mr Skripal’s Salisbury home was contaminated with Novichok on Sunday March 4.
Police said CCTV shows the two suspects in the vicinity of the property on that date.
Hours later, the men left the UK on a flight from Heathrow to Moscow – two days after they had arrived at Gatwick.
Metropolitan Police Assistant Commissioner Neil Basu said: “We have no evidence that they re-entered the UK after that date.”
He also confirmed that officers have now linked the attack on the Skripals to events in Amesbury four months later.
In the second incident, Dawn Sturgess, 44, and her partner Charlie Rowley, 48, were exposed to the same nerve agent used in Salisbury.
Ms Sturgess died in hospital in July, just over a week after the pair fell ill.
Mr Basu said: “We do not believe Dawn and Charlie were deliberately targeted, but became victims as a result of the recklessness in which such a toxic nerve agent was disposed of.
“We know that Novichok was applied to the Skripals’ front door in an area that is accessible to the public, which also endangered the lives of members of the public and emergency service responders.”
The charges announced on Wednesday relate to the first incident, but Mr Basu said officers continue to liaise with the CPS regarding the poisoning of Mr Rowley and Ms Sturgess.
Police also released an image of a counterfeit perfume bottle after tests found it contained a “significant amount” of Novichok.
Mr Rowley told officers he found a box he thought contained perfume in a charity bin on June 27.
Three days later he got some of the contents on himself, while Ms Sturgess applied some of the substance to her wrists.
Mr Basu said the manner in which the bottle and packaging was adapted makes it a “perfect cover” for smuggling the weapon into the country.
But he added: “We don’t yet know where the suspects disposed of the Novichok they used to attack the door, where Dawn and Charlie got the bottle that poisoned them, or if it is the same bottle used in both poisonings.”
Providing an in-depth update on an investigation he described as one of the most complex and intensive ever undertaken by counter-terror policing, Mr Basu also:
– Appealed for anyone who knows the two suspects or saw them while they were in the UK between Friday March 2 and Sunday March 4 to contact authorities;
– Published a detailed account of the movements of the two men over the three days, which included spending two nights at a hotel in east London and making a suspected “reconnaissance” trip to Salisbury the day before the Skripals were poisoned;
– Revealed tests carried out on the hotel room in Bow where the suspects had stayed showed contamination of Novichok but at levels below that which would cause public health concern;
– Said that despite meticulous and painstaking searches, although unlikely, it is impossible to guarantee there are no other materials linked to the incidents in Salisbury.
CPS director of legal services Sue Hemming said prosecutors in the service’s counter-terrorism division considered the evidence and concluded there was “sufficient evidence to provide a realistic prospect of conviction and it is clearly in the public interest” to charge Petrov and Boshirov with: conspiracy to murder Mr Skripal; attempted murder of Mr Skripal, Ms Skripal and Detective Sergeant Nick Bailey; use and possession of Novichok contrary to the Chemical Weapons Act; and causing grievous bodily harm with intent to Ms Skripal and Mr Bailey.
Ms Hemming said: “We will not be applying to Russia for the extradition of these men as the Russian constitution does not permit extradition of its own nationals.
“Russia has made this clear following requests for extradition in other cases. Should this position change then an extradition request would be made.
“We have, however, obtained a European Arrest Warrant which means that if either man travels to a country where an EAW is valid, they will be arrested and face extradition on these charges for which there is no statute of limitations.”
The case has echoes of the murder of Russian dissident Alexander Litvinenko in London in 2006.
In that case, two men were identified as suspects but Russia refused to hand them over.
Mr Skripal, 67, and his daughter were found unconscious on a bench in Salisbury city centre on March 4.
They spent weeks critically ill in hospital but have since been discharged.
Mr Bailey, who was involved in searching Mr Skripal’s home after the attack, was left seriously unwell. The officer continues to make good progress but remains off work, police said.
The events sparked a huge public health alert and plunged the UK Government’s relations with the Kremlin into crisis.
Moscow has repeatedly denied claims that Russia was behind the attempted assassination in March.
A senior adviser to Russian President Vladimir Putin said he does not know the people named as suspects by the UK security services.
President Putin’s foreign policy adviser, Yuri Ushakov, told reporters in Moscow that the names of the two Russian men suspected in the poisoning “do not mean anything to me”.
Mr Ushakov pointed to the fact that British authorities mentioned that they think the men’s names are aliases, and wondered “why this has been done and what kind of a message” Britain is trying to send to the Russian government.