Around 180 troops have been sent to Salisbury as the fallout from the attempted assassination on a Russian spy keeps growing.
Sergei Skripal, 66, and daughter Yulia remain critically ill in hospital after Sunday’s nerve gas attack.
The Met Police has summoned Royal Marines, RAF Regiment troops and chemical warfare specialists to help with its massive investigation.
Home Secretary Amber Rudd is chairing an urgent Cobra meeting in Westminster this afternoon, Downing Street said.
Detective Sergeant Nick Bailey, who was the first to respond, is also in a serious condition in hospital.
Police turned their attention on Friday to the cemetery where Mr Skripal’s wife and son were laid to rest.
Officers in hazmat suits were seen placing a blue forensic tent over his son’s memorial stone before appearing to stuff items in several yellow barrels.
According to the headstone, Mr Skripal’s wife Liudmila was 59-years-old when she died in October, 2012.
Her cause of death is believed to have been ‘disseminated endometrial carcinoma’, a type of cancer that begins in the womb.
Their son Alexander Skripal, 43, reportedly died in St Petersburg last July while on holiday with his girlfriend, after being struck down with liver failure.
His memorial stone was placed in the cemetery after his cremation.
It is thought their deaths are forming part of the Met Police Counter Terror team’s investigations into the attack.
Fears of chemical contamination have also seen Mr Skripal’s home cordoned off as detectives try to find out where they were first poisoned.
Suspicion is growing that Russia carried out the attempt on their lives as an act of revenge against the former intelligence officer, who was convicted in 2006 of selling state secrets to MI6.
He was later released as part of a spy swap with the US.
The Kremlin denies responsibility and British ministers have urged caution over saying who is to blame until the facts become clear.
Police said 21 people have been seen for medical treatment since the incident.
The figure includes members of the public and emergency staff, some of whom have had blood tests as well as receiving support and advice.