Ex-Russian spy may have been poisoned at home: U.K. police

British police said on Wednesday the former Russian double agent Sergei Skripal and his daughter may have been exposed to a suspected nerve agent at the front door of their home.

After this first known use of a chemical weapon on European soil since World War Two, Britain blamed Russian President Vladimir Putin for the attempted assassination and the West has expelled around 130 Russian diplomats.

Russia has denied any involvement in the attack and has said it suspects the British secret services of using the Novichok nerve agent, which was developed by the Soviet military, to frame Russia and stoke anti-Russian hysteria.

"Specialists have identified the highest concentration of the nerve agent, to date, as being on the front door of the address," a statement by Scotland Yard said.

"At this point in our investigation, we believe the Skripals first came into contact with the nerve agent from their front door," Dean Haydon, head of the Metropolitan Police's Counter Terrorism Command, was quoted as saying on the police website.

"We are therefore focusing much of our efforts in and around their address."

Skripal, 66, and his 33-year-old daughter Yulia have been in a critical condition since being found unconscious on a public bench in the English city of Salisbury on March 4. A British judge has said the two may have suffered permanent brain damage.

The attempted murder of Skripal, a former colonel in Russia's GRU military intelligence who betrayed dozens of Russian agents to Britain's MI6 spy service, has plunged Moscow's relations with the West to a new post-Cold War low.

After Britain expelled 23 Russians it said were spies working under diplomatic cover, Russia followed by throwing out 23 British diplomats. The United States, Canada and most member states of the European Union and NATO, expelled more than 100 diplomats.

British Foreign Secretary Boris Johnson said the Kremlin had underestimated the Western response to the attack on Skripal and his daughter, which also injured a British policeman. 

Johnson told an audience of ambassadors in London that 27 countries have now moved to expel Russian diplomats over Moscow's suspected involvement. 

"These expulsions represent a moment when a feeling has suddenly crystallised, when years of vexation and provocation have worn the collective patience to breaking point, and when across the world there are countries who are willing to say enough is enough," Johnson said. 

"If they (Russia) believed that we had become so morally weakened, so dependent on hydrocarbons, so chronically risk  averse and so fearful of Russia that we would not dare to respond, then this is their answer," he added.

Putin, who has been dealing with a deadly shopping centre fire in Siberia, has yet to respond, though Moscow has threatened to take retaliatory action.

"An analysis of all the circumstances … leads us to think of the possible involvement in it (the poisoning) of the British intelligence services," Russian foreign ministry said in a statement on Wednesday before the announcement by British police.

"If convincing evidence to the contrary is not presented to the Russian side we will consider that we are dealing with an attempt on the lives of our citizens as a result of a massive political provocation."

A London court last week gave permission for blood samples to be taken from the Skripals for examination by chemical 
weapons inspectors to confirm a conclusion by Britain that the military nerve agent had been used. 

An unidentified doctor who is treating the Skripals said they are both heavily sedated and unable to communicate, and  that it was not possible to assess when or to what extent either may regain mental capacity, according to the court's ruling.

After the United States broke a Russian spy ring in 2010, Skripal was exchanged for the 10 Russian spies caught in the United States.

Since emerging from the John le Carre-esque world of high espionage and betrayal, Skripal lived modestly in Salisbury and kept out of the spotlight until he was found unconscious on March 4.

His house in Salisbury was bought for $473,020 (260,000 pounds) in 2011. Skripal was listed as living there under his own name. In the years since he found refuge in Britain, Skripal lost both a wife and son.