Wiltshire Police declared a major incident in the early hours of Tuesday morning after two people collapsed in Amesbury following exposure to an “unknown substance”, triggering an investigation.

UPDATE 1300 — Samples sent to British chemical weapons research establishment Porton Down

Counter terror police are now investigating the incident, and samples of the unknown substance have been sent to the Porton Down laboratory — the same Wiltshire facility which was used to identify the nerve agent Novichok used in the attempted killing the Skripals in March. Britain’s Sky News reports Scotland Yard’s statement: “As you would expect, given the recent events in Salisbury, officers from the counter terrorism network are working jointly with colleagues from Wiltshire Police regarding the incident in Amesbury.

“As Wiltshire Police have stated, they are keeping an open mind as to the circumstances surrounding the incident and will update the public as soon and as regularly as possible.”

Areas cordoned off by police include a church, a chemist, and a new-build housing estate. They are beleived to be the last places the Amesbury pair visited before they took ill.

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The collapse of the pair — a man and a woman both in their 40s who are now in critical condition and receiving care in Salisbury Hospital — was initially linked to the abuse of “crack cocaine or heroin”, with emergency services suspecting a contaminated batch of drugs.

However, police later said in a statement that an “unknown substance” was suspected and a number of areas in Amesbury and nearby Salisbury have now been cordoned off by officers for public safety.

The affected couple were found on Saturday — meaning the potentially harmful unknown substance had not been subject to a cordon or proper decontamination efforts for up to four days after the initial discovery.

Wiltshire Police said Tuesday: “At this stage it is not yet clear if a crime has been committed. A police investigation has been established. In addition, a full multi-agency response has been co-ordinated.

“A number of scenes, believed to be the areas the individuals frequented in the period before they fell ill, will be cordoned off overnight in and around the Amesbury and Salisbury area as a precautionary measure.

“The public can expect to see an increased police presence in and around Amesbury and Salisbury.”

A Public Health England spokesman moved to reassure that despite the cordons, there was no threat to public health, saying: “The current advice from PHE England, based upon the number of casualties affected, is that it is not believed that there is a significant health risk to the wider public. This will be continually assessed as further information becomes known.”

The major incident has invited comparisons with the March 2018 poisoning of father and daughter Sergei and Yulia Skripal in nearby Salisbury. The former Russian spy, living in exile in the United Kingdom after release from a Russian prison, and his daughter were the targets of an apparent assassination attempt.

The British government claimed the substance used was the Cold-War era nerve agent Novichok and laid the blame for the attack on the Russian government. Much like the most recent collapses, the attack was initially thought to have been a serious drug overdose but was later declared a major incident after the first responding officer at the scene was hospitalised by exposure to the chemical.

The investigation and cleanup effort after the Skripal attack took over two months, with businesses across Salisbury finding themselves behind police lines forced to remain closed for extended periods.

This story is developing

Oliver JJ Lane is the editor of Breitbart London — Follow him on Twitter and Facebook