Deputy Assistant Commissioner Dean Haydon said: “At this point in our investigation, we believe the Skripals first came into contact with the nerve agent from their front door. We are therefore focusing much of our efforts in and around their address.”
He added: “I’d also like to thank the local community for their continued support and understanding.
“The unique circumstances of this investigation means that officers are likely be in the area for several weeks and months.”
The development came as Foreign Secretary Boris Johnson welcomed the collective expulsion of Russian diplomats in the wake of the Salisbury attack.
Speaking at the Lord Mayor of London’s Easter Banquet at Mansion House, in London, he said the fact that 27 countries “have themselves taken the risk of kicking out people whose presence they deem to be no longer conducive to the public good” was good news.
Mr Skripal and his daughter Yulia fell ill in Salisbury, Wiltshire, on March 4, apparently after being poisoned with a nerve agent. Russia has denied any involvement.
But Britain insists there is no plausible alternative explanation for the attack than to blame the Russians. Mr Johnson said it seemed the Kremlin had underestimated the strength of global feeling.
Mr Johnson said: “If they thought that the world had become so hardened and cynical as not to care about the use of chemical weapons in a peaceful place like Salisbury, if they believed that no one would give a fig about the suffering of Sergei and Yulia Skripal... then this is their answer.”
He paid tribute to the countries expelling diplomats because they know that their own Russia-based diplomats, and their families, must now deal with the possibility of their own lives being turned upside down.
Of the Russians, Mr Johnson said they had been claimed that Mr Skripal took an overdose, that he attempted suicide and therefore presumably tried to take his daughter with him, that his attempted murder was revenge for Britain’s supposed poisoning of Ivan the Terrible, or that we did it to “spoil the World Cup”.
“In fact the Foreign Office has so far counted 24 such ludicrous fibs – and so I am glad that 27 countries have stood up to say that they are not swallowing that nonsense any more,” he said.