The Home Secretary has said Britain would not be a "dumping ground for poison" as all eyes turned to Russia following a second nerve agent emergency in four month.

It comes after police say a couple who are critically ill may have been exposed to Novichok from handling a contaminated item.

Dawn Sturgess and Charlie Rowley are currently fighting for their lives in hospital after being poisoned by the toxic chemical substance in Amesbury, Wiltshire, at the weekend.

It follows the highly publicised attack on former Russian spy Sergei Skripal and his daughter Yulia in Salisbury in March.

Home Secretary Sajid Javid has demanded that the Kremlin provide an explanation for the two episodes, which investigators believe may be linked.

In a statement to the House of Commons, Mr Javid said: "The eyes of the world are currently on Russia, not least because of the World Cup.

"It is now time that the Russian state comes forward and explains exactly what has gone on."

Making clear that the UK will "stand up to the actions that threaten our security", he added: "It is completely unacceptable for our people to be either deliberate or accidental targets, or for our streets, our parks, our towns, to be dumping grounds for poison."

Mr Javid told MPs that he "cannot rule out" the possibility that the Novichok found in Amesbury was from the same batch used in the Salisbury attack.

However the Russian Embassy has hit back, accusing the Government of trying to "muddy the waters" and "frighten its own citizens".

Officers were called to a home in Muggleton Road on Saturday morning when 44-year-old Dawn Sturgess collapsed.

They were called back later that day when Charlie Rowley, 45, also fell ill.

Because the highest concentration of Novichok was found on the couple's hands, police believe the item they handled could be a container or reciprocal -- such as a vial or syringe -- used to transport the nerve agent for the initial attack on the Skripals and discarded in a public place.

Novichok remains highly toxic for a considerable period of time, so even the tiniest trace remaining in a container picked up by the victims could account for their severe illness.

It was initially believed that the two patients had possibly been using drugs from a contaminated batch, police said.

But after further tests, authorities declared a major incident and on Wednesday night counter-terror police assumed responsibility for the investigation after the Government's Porton Down laboratory concluded that the pair had been exposed to Novichok.

In a press conference, Chief Constable Kier Pritchard of Wiltshire Police defended his force's initial response, saying that he "fully supports" the decisions taken by officers who thought the couple had initially fallen ill after taking illegal drugs.

Amid questions about the post-Salisbury clean-up operation, Home Secretary Javid said the risk to the public remained low.

He added: "We have taken a very robust approach to decontamination and there is no evidence that either the man or the woman in hospital visited any of the places that were visited by the Skripals.

"Our strong working assumption is that the couple came into contact with the nerve agent in a different location to the sites which have been part of the original clean-up operation."

Earlier yesterday, Security Minister Ben Wallace said the Amesbury couple were not directly targeted.

Mr Wallace told BBC Radio 4's Today programme: "The working assumption would be that these are victims of either the consequence of the previous attack, or something else, but not that they were directly targeted."

Linking the incident to the attack on the Skripals, Mr Wallace said: "I think what we said at the time was that this was a brazen and reckless attack in the heart of a very peaceful part of the United Kingdom, and that is part of the anger I feel about the Russian state is that they chose to use clearly a very, very toxic, highly dangerous weapon."

Prime Minister Theresa May declared that Salisbury is "very much open for business" after residents raised fears that the new case will hamper the local economy.

The Met said that around 100 detectives from the Counter Terrorism Network are working alongside colleagues from Wiltshire police.

Six sites visited by Mr Rowley and Ms Sturgess before they fell ill have been cordoned off. Police have extended this to include all of Muggleton Road and outside the supported living where Ms Sturgess lived.

Debbie Stark, deputy director for Public Health England in the South West, said that anyone who may have been in any of the cordoned-off areas after 10pm last Friday should take some precautionary measures about washing clothing and cleaning jewellery.

The episode in Salisbury - the first use of a nerve agent in Europe since the Second World War - sparked international outrage.

Mr Skripal and his daughter have since left hospital.

A Russian Embassy spokesman said: "All allegations of Russia's involvement in the incidents in Salisbury and Amesbury are merely speculative and are not based on objective data of the investigation."