Police have confirmed that two people who fell ill in southern England on Tuesday had been exposed to Novichok — the same substance that poisoned an ex-Russian spy Sergei Skripal and his daughter Yulia in nearby Salisbury in March.

Wiltshire Police declared a major incident on Tuesday evening after it was suspected that a local man and woman, being treated in hospital, might have been exposed to an "unknown substance."

Paramedics were called to an address in Muggleton Road, Amesbury, on Saturday morning (June 30) after a woman, 44, collapsed at the property. They were then called back later that day to tend to a man, 45, who had also fallen ill.

The pair are believed to be Charlie Rowley and Dawn Sturgess. They are both Wiltshire locals and British nationals, are being treated at Salisbury District Hospital. They remain in a critical condition.

It was initially thought the two patients fell ill after using heroin or crack cocaine from a contaminated batch of drugs.

Police said they are keeping an open mind as to the circumstances surrounding this incident.

A police investigation has been established in addition to the coordination of a full multi-agency response, according to authorities.

A Public Health England (PHE) spokesman said: "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 statement said the public can "expect to see an increased police presence in and around Amesbury and Salisbury".

Salisbury District Hospital was open as usual and advised people to still attend routine appointments unless they are contacted to state otherwise.

Britain's interior minister said he would chair a meeting of the government's emergency committee on Thursday to discuss the exposure of two people in southern England to the nerve agent Novichok.

"(This) follows the reckless and barbaric attack which took place in Salisbury in March," Sajid Javid said in a statement.

"Tomorrow I will chair a meeting of the government's emergency committee COBR in relation to the ongoing investigation."