A senior British minister called Wednesday for “cool heads” over the suspected poisoning of a former Russian double agent, as Moscow accused politicians and journalists of whipping up anti-Russian sentiment.

After chairing an emergency government meeting to discuss the situation of Sergei Skripal, interior minister Amber Rudd said police were closer to identifying the substance that he was exposed to.

The 66-year-old Russian, who moved to Britain in a 2010 spy swap, is in a critical condition in hospital along with his daughter Yulia after they collapsed on a bench outside a shopping centre in the southwestern English city of Salisbury on Sunday.

“We do know more about the substance and the police will be making a further statement this afternoon,” Rudd said.

“We need to keep a cool head,” she stressed, adding that investigation would “respond to evidence, not to rumour”.

Police say they are keeping an open mind about what happened, but Foreign Secretary Boris Johnson on Tuesday pointed the finger at Russia.

He noted the “echoes” with the 2006 poisoning in London of former Russian spy and Kremlin critic Alexander Litvinenko, which Britain has blamed on Moscow.

The Kremlin hit back on Wednesday, with foreign ministry spokeswoman Maria Zakharova telling reporters the story “was straight away used to boost an anti-Russian campaign in the media”.

Zakharova earlier said Johnson’s comments were “wild” and “words of savagery”.

National counter-terrorism police have taken control of the case, citing the “unusual circumstances”, and opened up a new crime scene on Wednesday in the nearby town of Amesbury.

“The focus at this time is to establish what has caused these people to become critically ill,” said the head of the unit, assistant commissioner Mark Rowley.

Skripal and his 33-year-old daughter had lunch at a nearby restaurant before walking to the shopping centre, where witnesses said they appeared “out of it”.

Experts said the circumstances appeared to rule out radiation poisoning, as in Litvinenko’s case.

“Radiation poisoning tends to take tens of hours to several days to show symptoms after exposure,” said Professor Malcolm Sperrin, a medical physics expert with the state-run National Health Service (NHS).

“This may have been chemical, but we can’t be sure.”

Police reportedly took away the table and chairs where Skripal and his daughter were sitting in Zizzi’s restaurant for analysis.

Some emergency services personnel who treated the pair required medical treatment, and The Sun tabloid reported that two police officers had itchy eyes, wheezing and rashes.

Newspaper reports speculated on the use of thallium, which dissolves in water and is odourless and tasteless, or the banned VX nerve agent used on the half brother of North Korean leader Kim Jong Un.

The BBC reported that without knowing the cause, the hospital treating Skripal and his daughter could only treat their symptoms, citing one source as saying that he “is not in a good way at all”.

Prime Minister Theresa May was updated on the situation at a meeting of her national security council on Tuesday afternoon, but she has declined to publicly comment on an ongoing police investigation.

But in an address to the House of Commons on Tuesday, Johnson made several references to Russia, and said Britain would respond “appropriately and robustly” if a government was found responsible.

Skripal was a former colonel in Russian military intelligence who was jailed in his country for betraying agents to Britain’s MI6 secret service.

He was pardoned before being flown to Britain as part of a high-profile spy swap involving Russia and the United States in 2010, and has kept a low profile since.

The Times newspaper reported that police would look into the 2012 death of Skripal’s wife from cancer, and that of his 44-year-old son last year in St Petersburg, reportedly from liver problems. (AFP)