A major incident was declared at a hospital when people fell ill after being exposed to a risky substance thought to be the synthetic opioid fentanyl.
One of the two people in critical condition is a former Russian double agent convicted of treason in Moscow for betraying dozens of spies to British intelligence, two sources close to the investigation told Reuters.
The closure was linked to the admission to the hospital on Sunday of a man and a woman who were found collapsed in Salisbury's Maltings shopping centre.
The A&E department at Salisbury District Hospital was closed to the public earlier today and fire-fighters were called to decontaminate the area.
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"At this stage it is not yet clear if a crime has been committed and a multi-agency response has been co-ordinated".
Zizzi, on Castle Street, has been sealed by Wiltshire Police "as a precaution".
Public Health England say there's not thought to be any risk to the public.
"We would like to take this opportunity to thank members of the public who have assisted us so far and respected the cordons which remain in place". We are asking local people to use the walk in centre on Avon Approach for non emergency conditions.