The statement of unity came ahead of angry clashes at the United Nations Security Council in NY after British diplomats raised the allegations.
British authorities have said the men were Russian military intelligence agents travelling with genuine Russian passports, but under aliases.
She said the poisoning was "not a rogue operation" and was "almost certainly" approved at a senior level of the Russian state.
"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", said Sue Hemming, director of Legal Services at the Crown Prosecution Service.
Russian Federation does not extradite its nationals, but a European Arrest Warrant has been obtained in case the men travel to the EU.
Prosecutors did not release charges relating to the death of Dawn Sturgess, a woman who died in the Salisbury region after coming into contact with a discarded Novichok bottle several months after the Skripal poisonings, nor to the poisoning of her partner Charlie Rowley, who survived.
Ruslan Boshirov (L) and Alexander Petrov.
"Today marks the most significant moment so far in what has been one of the most complex and intensive investigations we have undertaken in Counter Terrorism policing; the charging of two suspects - both Russian nationals - in relation to the attack on Sergei and Yulia Skripal", Scotland Yard Assistant Commissioner Neil Basu said in a statement.
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Leaders of the US, France, Germany and Canada have said they have "full confidence" in the UK's conclusion that the two Salisbury poisoning suspects were members of Russia's GRU intelligence service. "The GRU is a highly disciplined organisation with a well-established chain of command", she said. GRU agents are also operating on the ground in Syria, where they help direct Russian airstrikes. "It was nearly certainly also approved outside the GRU at a senior level of the Russian state". Police appealed for anybody who knows or recognizes the men to come forward with information.
Hours later, the men left the United Kingdom on a flight from Heathrow to Moscow - two days after they had arrived at Gatwick.
Leonid Slutsky, chairman of the Foreign Affairs Committee of the State Duma, the lower chamber of Russia's parliament, dismissed the British investigation as an "anti-Russian provocation".
Britain blamed Russian Federation for the poisonings and identified the poison as Novichok, a deadly group of nerve agents developed by the Soviet military in the 1970s and 1980s.
Basu said the two men had been filmed by CCTV cameras near Skripal's house, where Novichok was sprayed on the front door. The first ambulance for Skripal and his daughter was called at 4.15 p.m. that afternoon.
"We will uphold the prohibition of chemical weapons".
Vassily Nebenzia told the U.N. Security Council on Thursday that Britain's claim that two agents from Russia's special intelligence services tried to murder Sergei Skripal and his daughter in the southern England town of Salisbury with a military-grade nerve agent is an invention "out of thin air", riddled with inconsistencies. Bailey was sickened after attending to the Skripals where they were found in Salisbury. It had been held in a pink box, falsely labeled as Nina Ricci Premier Jour perfume.