They remain in critical condition in hospital.
Previously, the leaders of France, Germany, the US and the UK have issued a joint statement blaming Russia for the nerve agent attack in Salisbury as Moscow said it will expel British diplomats in retaliation for Theresa May's action against the Kremlin, the Daily Telegraph UK reports.
Emmanuel Macron, Angela Merkel and Donald Trump - the leaders of three of the UK's most important allies - said they agreed with the Prime Minister's assessment that there was "no plausible alternative explanation" for the attack.
The joint statement represents a major boost for Mrs May and comes one day after she moved to expel 23 Russian diplomats and suspended high-level contact with Moscow in response to the Salisbury incident.
The statement, issued by Downing Street, said: "The United Kingdom briefed thoroughly its allies that it was highly likely that Russia was responsible for the attack.
"We share the UK assessment that there is no plausible alternative explanation, and note that Russia's failure to address the legitimate request by the UK government further underlines its responsibility.
"We call on Russia to address all questions related to the attack in Salisbury."
The statement was issued as Mrs May visited the scene of the attack in Salisbury.
Speaking as she met emergency services, Mrs May said: "We do hold Russia culpable for this brazen and despicable act that has taken place on the streets of what is such a remarkable city."
Meanwhile, Sergei Lavrov, the Russian foreign minister who the Prime Minister said would be barred from coming to the UK, said the Government's response was prompted by Brexit as he branded the measures "absolutely boorish".
Russia has repeatedly denied it is responsible for the attack, which left former spy Sergei Skripal and his daughter in a critical condition in hospital.
But Boris Johnson, the Foreign Secretary, who met Mr Lavrov in December last year, accused Russia of seeking to deny responsibility while taking "glory in it".
Speaking at the United Nations meeting last night the Russian representative said his country had never made or researched how to make the specific nerve agent involved.
It followed a claim made by Jeremy Corbyn's spokesman Seumas Milne that the Novichok nerve agent could have got into "random hands" after the break up of the Soviet Union.
Asked at a forum whether Russia would expel British diplomats, Mr Lavrov said "definitely", state news agency RIA Novosti reported. Asked when this would occur, he said "soon".
On Thursday, America announced new sanctions against Russia for election meddling and cyber-attacks as the administration vowed to punish the country's "nefarious attacks".
Nineteen people and five Russian organisations were targeted in what amounts to the most significant action against Moscow since Donald Trump took office.
Russia's spying agency the Federal Security Service (FSS), the successor to the KGB, was among those bodies hit and was accused of targeting White House and military officials.
The actions punished by the sanctions pre-dated the Salisbury attack but Steven Mnuchin, the US treasury secretary, said it was part of a "broader effort" to address "nefarious attacks" from Russia.
Meanwhile Mr Trump said he was in "deep discussions" with Mrs May over the Salisbury attack and said "it certainly looks like the Russians were behind it".
It came as France rowed back after failing to condemn the Kremlin's actions on Wednesday night, despite Mrs May's announcement that Russia was behind the breach of international law.
President Macron phoned the Prime Minister on Thursday morning and expressed solidarity as he said France "shares the UK's conclusions" that Russia is responsible.
Previously a spokesman for Mr Macron called Mrs May's decision to expel 23 Russian diplomats, thought to be undercover intelligence agents, "fantasy politics" and refused to publicly state who was to blame.
The decision prompted an international backlash as the former secretary general of Nato, Anders Fogh Rasmussen, said that "anything short of full solidarity with the UK now would be seen as a victory by the Kremlin".
He added: "I don't think the Russians have given any convincing answers on how a Soviet era nerve toxin ended up striking down a former double agent.
"Either the Russian Government is directly responsible for this atrocity or they are responsible for the loss of security in Russia and in both cases it is a violation of international law."
Mr Rasmussen said invoking Article 5 in support of collective defence would be "disproportionate" but he added that every EU nation has experienced Russian aggression in some form and "now is the time to fight back".
Asked about the French position, Mr Johnson appeared to shrug off the lack of support, telling BBC Radio 4's Today programme that "different French spokesman have said different things at different times".
In a morning of fast-paced developments on the issue Mr Johnson told the BBC that the Government is already going after the money of Russians living in the UK.
It followed criticism of the Prime Minister's decision not to announce tougher financial sanctions in her initial response on Wednesday, although Downing Street has made clear that further action can and will be taken if necessary.
Mr Johnson said the Government is using powers to freeze assets but warned the UK will not act outside of the law in response to the attack.
He said: "We will go after the money and actually we are going after the money ... we have the Criminal Finance Act which allows us to put unexplained wealth orders on people ... work is underway to do that."
Speaking to BBC Radio 4's Today programme Mr Johnson added that England should not boycott the World Cup but would not send dignitaries and said British people should not fear a second Cold War despite strong action against the Kremlin.
He said: "I don't think the British people have any reason to be nervous, this is not going to be another Cold War in the sense we remember, what seemed to be an existential threat ... we faced the possibility of thermo-nuclear conflict and I don't believe that is on the cards today thank heavens.
"But it is quite true that Russia ... feels that she has been belittled since the fall of the Berlin wall ... President Putin feels the ghost of Stalin, he sees Nato on his borders ... he feels an incredible sense that this great country has been diminished and that's why he's causing trouble in the Western Balkans ... one of the reasons why the UK is so much the object of his indignation is that we are the country that sticks up for our values."
Mr Johnson said the evidence of Russian guilt was "overwhelming" because only Moscow had access to the poison used and a motive for harming Mr Skripal.
"There is something in the kind of smug, sarcastic response that we're heard from the Russians that to me betokens their fundamental guilt," he told the BBC.
"They want to simultaneously deny it and yet at the same time to glory in it."
- AP, Daily Telegraph UK
