The British investigation into the nerve agent attack in Salisbury believes the poison was smeared on to the door of the victims’ house no more than 24 hours before they collapsed.

Scotland Yard’s counter-terrorism command and the security services are running the inquiry into the 4 March attack on the former Russian spy, Sergei Skripal, and his daughter Yulia with military grade nerve agent associated with Moscow.

The Guardian has learned that their investigation has narrowed down the time when the poison was smeared on to the front door of Skripal’s Salisbury home.

Investigators believe it was placed there after his daughter arrived at the home on Saturday 3 March, having flown to the UK from Russia.

She did not leave until 9.15am on Sunday, when she and her father got into his car and drove to a location in Salisbury. By 4.15pm that day, the pair were found on a bench in Salisbury town centre, gravely ill.

Being able to narrow down the time when the poison was placed on the door has allowed investigators to concentrate resources as they race to identify those responsible.

DS Nick Bailey was later was poisoned by the nerve agent when he and other officers attended Skripal’s home looking for evidence, including signs of drug use or suicide notes, according to the chief constable of Wiltshire police.

Kier Pritchard told the Salisbury Journal that Bailey was one of a team of officers who attended Skripal’s home on 4 March. He said the group underwent a “decontamination process” at the town’s district hospital overnight on Sunday and into Monday morning, after details of the attack became clearer.

Deputy assistant commissioner Dean Haydon, senior national coordinator for counter-terrorism, said: “Our enquiries are focused around the people and vehicles that were in the vicinity of the Skripal’s address and leading up to where they fell ill in the Maltings. We would ask anyone who may have information, or who may have seen or heard something – however small – to contact police on 101.”

Police said that 100 counter-terrorism officers remain in Salisbury to continue the investigation. British authorities strongly believe that those responsible are connected to Russia, but the Kremlin denies all responsibility.

The nerve agent novichok was used in the attack, which had been expected to be fatal. While Bailey was discharged from hospital after about a fortnight, the Skripals spent many weeks in hospital and are now recovering.