One of the Russianchemical weapons scientists who developed the Novichoknerve agent has warned that hundreds of people could be at risk for years following the attack in Salisbury.
Dr Vil Mirzayanov, who fled to the US two decades ago, claimed Sergei Skripaland his daughter would not recover from the poisoning.
“There is no cure,” he told Sky News from his home in New Jersey. “There are antidotes but…they will be invalid for whole life.”
Dr Mirzayanov said Novichok was so powerful that extremely small doses could remain a danger to public health for years.
“I suppose it’s very bad because even the very small doses, very small, still they are very effective and then there will be consequences for years probably,” he added.
The scientist said public health advice, including washing clothes and sealing belongings was “not enough” and confirmed that hundreds of people could be at risk.
Asked whether he felt guilty for his part in developing Novichok, he added: “I participated in this criminal enterprise, because of that I’m probably the most fiery enemy of these chemical weapons.
“It’s a weapon of mass murder.”
The warning came as the Government sought to reassure the public that the wider risk from the attack on 4 March remained low.
Public Health England issued advice for people who visited The Mill pub and Zizzi restaurant, where Mr Skripal and his daughter ate and drank before falling ill, to wash their clothes and belongings, and seal off anything that cannot be manually cleaned.
Neil Basu, Assistant Commissioner of the Metropolitan Police, said 38 people had been seen by doctors in relation to the incident.
He told a press conference that 34 of those patients had been assessed and discharged, with Mr Skripal, his daughter and Detective Sergeant Nick Bailey remaining in hospital and one person being monitored as an outpatient.
The officer said anyone known to have been in the same area as the victims has been directly contacted, adding: “This is over a week later – people are not presenting symptoms, we are not seeing them.”
Mr Basu said he could not comment on how the nerve agent was administered but vowed that police would leave “no stone unturned in establishing the full circumstance of the attack”.
He issued a new appeal for anyone who saw the pair in Mr Skripal’s car – a red BMW – in Salisbury between 1pm and 1.45pm on the day of the attack to call police.
Ms Skripal had arrived at Heathrow to visit her father the previous day, and they arrived in the Sainsbury’s upper level car park in The Maltings at 1.40pm.
They went to The Mill pub before going to Zizzi’s for lunch, arriving at 2.20pm and leaving at 3.35pm.
Mr Skripal and his daughter were caught on CCTV leaving the restaurant on foot minutes later, and emergency services received the first report from members of the public who saw them slumped on a bench at 4.15pm.
Theresa May has named Russia as the likely culprit behind the attack, because of its development of Novichok and “record of conducting state-sponsored assassinations”, including against defectors like Mr Skripal who are viewed as legitimate targets.
“Either this was a direct act by the Russian state against our country, or the Russian government lost control of this potentially catastrophically damaging nerve agent and allowed it to get into the hands of others,” she told MPs on Monday.
“This attempted murder using a weapons-grade nerve agent in a British town was not just a crime against the Skripals.
“It was an indiscriminate and reckless act against the United Kingdom, putting the lives of innocent civilians at risk, and we will not tolerate such a brazen attempt to murder innocent civilians on our soil.”
The Russian government has denied involvement in the attack and said it willignore the Prime Minister's midnight ultimatumunless it is given samples of the nerve agent used.
Mr Skripal was jailed for “treason” by Russia in 2006, after working as a double agent for MI6 during his time as a colonel in the GRU military intelligence service.
He was released early in 2010, following a high-profile “spy swap,” with Russian sleeper agents uncovered in the US and given refuge in the UK and British citizenship.
Mr Skripal appeared to lead a quiet life in Salisbury but sources told The Independent he may have come to the attention of powerful enemies in Russia by “freelancing” for private intelligence firms run by former MI5, MI6 and GCHQ agents.
They insisted he was not an active MI6 asset and was not viewed as being under threat.
Ms Skripal, 33, lived with her parents in Salisbury before her mother died in 2012, when the death was recorded as endometrial cancer.
According to her Facebook profile, she worked at a Holiday Inn in Southampton in 2014, before moving back to Moscow and working for PepsiCo Russia.