About 180 military personnel have been deployed to Salisbury to help in the investigation into the attempted murder of an ex-Russian spy and his daughter.
The military personnel - drawn mostly from the Army, but also from the Royal Marines and RAF - are experts in chemical warfare and decontamination.
Sergei Skripal and his daughter Yulia collapsed on Sunday afternoon after being exposed to a nerve agent.
Home Secretary Amber Rudd has described the attack as "outrageous".
Those deployed include instructors from the Defence Chemical Biological Radiological and Nuclear Centre and the 29 Explosive Ordnance Group, who are experts in bomb disposal.
The military has also sent 18 vehicles.
The Metropolitan Police said the counter-terrorism unit has requested the military's assistance "to remove a number of vehicles and objects from the scene", including ambulances that may have been contaminated while assisting the victims.
The public should not be alarmed and there is no evidence to suggest a wide public health risk at this time, the police added.
Valery Morozov, a Russian exile, told BBC News that Mr Skripal was working in cyber security.
The former Russian military security colonel and his daughter remain in a critical condition at Salisbury District Hospital.
Det Sgt Nick Bailey - who attended the scene on Sunday - is conscious but "very anxious" about being exposed to a nerve agent.
Director of nursing Lorna Wilkinson said Mr Bailey was in a serious but stable condition.
Specialist investigators wearing protective suits have been seen examining the bench that Mr Skripal and his daughter collapsed on.
Mr Skripal's house and his car have also been cordoned off.
It is known that Mr Skripal and his daughter had visited the Mill pub and Zizzi restaurant in Salisbury on Sunday afternoon, before they were found near the Maltings shopping centre.
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