The Amesbury couple exposed to the nerve agent Novichok “must have got a high dose”, the head of the UK’s counter-terrorism police said on Monday. 

Speaking ahead of an emergency Cobra meeting at 1pm, Assistant Commissioner Neil Basu said the investigators’ “hypothesis” is that Dawn Sturgess, who died in hospital on Sunday evening, and her partner Charlie Rowley “must have handled a container that we are now seeking”.

Basu said police were unable to say if the nerve agent that killed Sturgess, 44, and left 45-year-old Rowley in a critical condition in hospital is linked to the March 4 attack on former Russian spy Sergei Skripal and his daughter, Yulia, in Salisbury.

“However, this remains our main line of inquiry,” he said. 

The decision to link the two attacks on Monday increases pressure on Russia, which has denied all responsibility for the attack on the Skripals despite considerable pressure from the British government and internationally.  

Home Secretary Sajid Javid is due to update MPs in the Commons on Monday about the case, after chairing a meeting of the government’s Cobra emergencies committee. 

Russia has said it was sorry to hear of Sturgess’s death.

Basu added that there was no evidence to suggest the couple had visited any of the Salisbury sites that were decontaminated in the four months since the Skripals fell ill.

Detailed searches are continuing at Sturgess’s address at John Baker House, Salisbury and Rowley’s home in Muggleton Road, Amesbury, along with Queen Elizabeth Gardens in Salisbury.

“Our focus and priority is to find and identify any container that we think might be the source of this contamination,” Basu said, saying that the couple’s reaction to the exposure was “so severe” that they must have got a “high dose” of the nerve agent that kept the Skripals hospitalised for months. 

Asked about the whereabouts of the container and if it could have been discarded somewhere, Chief Constable of Wiltshire Police, Kier Pritchard, said the that was of “real concern for us all”.

Basu said police had detailed the couple’s movements in the days before they were hospitalised on June 30 and as a consequence a red Ford transit van Rowley had travelled in on the day he fell ill was now being tested at Porton Down as a “precautionary measure”.

“This is crucial to our understanding,” he said.

Three other people who were travelling in the vehicle, Basu said, had been identified and contacted. None were showing signs of having been exposed to a nerve agent, he said. 

Basu reiterated that there was no immediate risk to members of the public, but urged those living in Amesbury and Salisbury to avoid picking up “strange items” like needles, syringes and “unusual containers”. 

Since the attempted murders of the Skripals, 21 people had presented with medical “concerns”, Basu said, but all were screened and shown to be “all clear”. 

Basu said the death of mother-of-three Sturgess, “only serves to strengthen the resolve of our investigation team as we work to identify those responsible for this outrageous, reckless and barbaric act”.

A relative at Sturgess’s family home in Durrington, near Amesbury, said the family was “devastated” but declined to comment further.

On Monday floral tributes began to appear at a cordon outside Sturgess’s home and in Salisbury city centre.

One card read: “RIP Dawn, You were the innocent one in this. Heart goes out to your family and children. Good night sweetheart xxxxxx.”

Another said: “Dawn, Always in our thoughts. Love from the people of Salisbury.”

In a second press conference, Wiltshire police said that Sturgess was an “innocent member of the public who should have been able to go about her daily life without becoming an unwilling victim in such an unprecedented, international, incident.”

Police and Crime Commissioner Angus Macpherson said they were “horrified and appalled that an illegal and lethal nerve agent has been used on the streets of our county. And while the city of Salisbury has bounced back so resiliently, it saddens me greatly that Sturgess, and now her family, are bearing the devastating impact of this incident.”

The Kremlin has suggested that any suggestion Russia was involved would be absurd, describing the investigation into Sturgess’s death as a British problem.

Speaking in the Commons, the prime minister said on Monday: “I am sure the House will join me in sending our deepest condolences to the family and friends of Dawn Sturgess who passed away last night. 

“The police and security services are working urgently to establish the full facts in what now is a murder investigation.

“I want to pay tribute to the dedication of staff at Salisbury District Hospital for their tireless work in responding to this appalling crime.

“Our thoughts are also with the people of Salisbury and Amesbury, and the home secretary will make a statement shortly including on the support we will continue to provide to the local community throughout this difficult time.”  

Javid told the Commons that it had not been possible to identify or determine if the poison in the Amesbury incident was from the same batch of Novichok that was used in the attack on the Skripals.

“The scientists have not been able to identify or determine if it is the same batch – it may well be but at this point that is not known.

“That’s partly because the sample that the scientists have at this point at Porton Down from this incident has come from blood samples from the two individuals that have been contaminated and it’s not enough of strength of sample so to speak to match it in terms of batch.

“If there is further evidence available later on through the investigation that might well be possible.”

Defence Secretary Gavin Williamson, replying to Conservative MP Michelle Donelan in the Commons, said: “The simple reality is that Russia has committed an attack on British soil which has seen the death of a British citizen.

“That is something that I think the world will unite with us in actually condemning.”

He also said the Ministry of Defence is working “incredibly closely” with the police on the investigation and the clear-up effort, adding 175 armed forces personnel are involved.

KEY QUESTIONS

– What has happened?

Dawn Sturgess, 44, died on Sunday after being exposed to a nerve agent.

Charlie Rowley, 45, who was also exposed to the nerve agent, is critically ill in hospital.

– How did they come into contact with the nerve agent?

Police have said they were exposed after touching a contaminated item with their hands.

– Have police found the item?

Not yet. On Sunday police said detectives were working “as quickly and as diligently as possible to identify the source of the contamination, but this has not been established at this time”.

– Have the authorities linked Amesbury to the Salisbury case?

Not yet, although the signs are that the investigation is moving in that direction. The possibility that the two investigations might be linked is “clearly a key line of inquiry”, Scotland Yard said.

– Was the nerve agent at the centre of the Amesbury alert the same type as the one used in Salisbury?

Yes, in both cases tests by Government experts detected Novichok, a highly potent nerve agent.

– Is the substance found in Amesbury from the same batch?

This has not been established either way. On Sunday, police said they are “not in a position to say whether the nerve agent was from the same batch that the Skripals were exposed to”.

– Did Sturgess and Rowley go to any of the same locations as the Skripals?

There is no evidence that they visited any of the sites decontaminated following the attempted murders of Sergei and Yulia Skripal in March, according to investigators.

– Who was responsible for the Salisbury attack?

The UK Government has pointed the finger at the Russian government – an allegation the Kremlin denies.

– Has anyone been identified as a suspect in that case?

Not publicly. Police say their “complex” investigation remains ongoing.