Sergei and Yulia Skripal first came into contact with novichok at their home address, detectives believe.
Specialists have identified the highest concentration of the nerve agent on the front door of the address.
Detectives will continue to focus their enquiries around the home address for the coming weeks, and possibly months, as the investigation continues.
In a statement from the Metropolitan police, the force say officers will be carrying out thorough searches in the areas surrounding this former spy’s home. The searches will be part of the ongoing investigation as well as a precautionary measure.
At this point in our investigation, we believe the Skripals first came into contact with the nerve agent from their front door, deputy assistant commissioner Dean Haydon, Senior National Coordinator for Counter Terrorism Policing said.
We are therefore focusing much of our efforts in and around their address. Those living in the Skripals neighbourhood can expect to see officers carrying out searches as part of this but I want to reassure them that the risk remains low and our searches are precautionary, he added.
Traces of the nerve agent have been found at some of the other scenes detectives have been working at over the past few weeks, but at lower concentrations to that found at the home address.
A dozen policemen, who were not wearing protective overalls, searched an alley beside the victim’s house on Wednesday for what is thought to be the first time.
The investigation into who poisoned Mr Skripal, 66, and his daughter, 33, is one of the largest and most complex investigations undertaken by British counter terrorism police.
The pair were found collapsed on a bench on Sunday March 4 in a critical state.
Around 250 counter terrorism detectives are working around the clock on the investigation, according to the Met police.
More than 5,000 hours of CCTV is being examined and more than 1,350 pieces of evidence are being scrutinised.
Around 500 witnesses have been identified and hundreds of statements taken.
On Wednesday, the 24th day of the investigation, Mr Haydon thanked the local community “for their continued support and understanding.”
Specialist search officers are concluding their work at some of the locations involved in the investigation and turning the areas over to Wiltshire Police.
These areas include the London Road Cemetery where investigators in hazmat suits were seen early on in the case.
The UK has accused Russia of the attack, resulting in more than 150 Russian diplomats being expelled from countries across the globe.
Russia rejects the accusation and has challenged the UK to prove the British intelligence services did not conduct the assassination attempt.
The best friend of Mr Skripal told Sky News he believes the poisoned double agent and his daughter are so critically ill they should be allowed to die.