The revelation comes days after the identities of the men suspected of the failed hit were given as Ruslan Borishov and Alexander Petrov – though they are believed to be assumed names.
The Sunday Mirror can reveal authorities are keeping a close hold on details of the other two suspects.
A Whitehall insider said the medic may have been involved to prevent cross-contamination – or even to make sure the NHS and police did not need to be involved if one of the hitmen was accidentally poisoned.
The source said Petrov and Borishov – who claim to be tourists – could have met up with the other two suspects after checking into the City Stay Hotel on Bow Road in East London.
They later caught trains from Waterloo to Salisbury, where the deadly Novichok was daubed on the door of the house where Skripal and daughter Yulia lived.
The source said: "It’s believed they could have met a handler who was working at the embassy and a fourth, the medic, might have had oversight of the whole thing to make sure they didn’t risk ruining the operation by getting themselves contaminated."
Other sources yesterday said police know the real ID of Petrov and Borishov.
An insider said: "They’ve had hundreds of officers trawling CCTV and the facial recognition software meant they could match them with passports used in the years leading up to the attack."
In Thursday's interview to the state-funded RT, Alexander Petrov and Ruslan Boshirov, the two Russians charged with perpetrating nerve agent attack in British Salisbury have claimed they were visiting the town's "famous" cathedral as tourists.
Petrov and Boshirov have been charged with attempting to murder of former Russian spy Sergei Skripaland his daughter Yulia in Salisbury in March by spraying Novichok nerve agent on the handle of their door. Scotland Yard have said these names are probably aliases.
A UK government spokesman rubbished the men's claims as "obfuscation and lies", while John Glen, the Conservative MP for Salisbury and South Wiltshire, called the statements "not credible".
Russian President Vladimir Putin said Russia knew the real identity of two men accused by British prosecutors of trying to murder Skripals and that they were civilians with nothing criminal about them.
Russia adamantly denies involvement in the poisoning, which had added to severe strains in ties between Russia and the West.
Putin's declaration came seven days after British authorities announced that they had charged two Russian men, identified as Aleksandr Petrov and Ruslan Boshirov, with carrying out the poisioning on March 4.
They accused the pair of smuggling the Soviet-designed nerve agent Novichok into Britain in a fake perfume flask and smearing some of the substance on the front door of Sergei Skripal's home in the English city of Salisbury, where the former GRU officer settled after being sent to the West in a Cold War-style spy swap in 2010.
Putin made no comment about whether the names they used were real.
The attack left Sergei Skripal, 67, and Yulia Skripal, 34, in critical condition, but both have recovered after weeks in the hospital.
A couple who authorities said found the perfume bottle after it was discarded by the attackers fared worse: Charlie Rowley recovered after treatment in the hospital but his partner, Dawn Sturgess, 44, died on July 8.
British authorities have said that a European arrest warrant has been issued for the two Russians, who they suspect were using aliases.