What we know (and don't know) about the Amesbury poisoning

The Amesbury emergency has prompted a raft of questions about the incident, the nerve agent involved, and whether there is any link to the Salisbury attack in March.

- What has happened?
A couple are critically ill after being exposed to the Novichok nerve agent.

- How did they come into contact with the nerve agent?
This is one of the key strands of a major investigation, and no definitive explanation has yet been given publicly. One theory understood to be under investigation is that the pair who were poisoned in the latest incident may have inadvertently found a container - such as a phial or syringe - used to transport the nerve agent for the attack on a former Russian spy and his daughter in Salisbury in March.

- Were the couple poisoned in Amesbury deliberately targeted?
No, according to security minister Ben Wallace. He said: "The working assumption would be that these are victims of either the consequence of the previous attack, or something else."

- Have authorities conclusively linked Amesbury to the Salisbury case?
Not yet, although the signs are that the investigation is moving in that direction. Home Secretary Sajid Javid described a possible connection as the "leading line of inquiry" but warned against jumping to conclusions.

- Was the nerve agent at the centre of the Amesbury alert the same type as the one used in Salisbury?
Yes, in both cases tests by government experts detected Novichok, a highly potent nerve agent.

- Is the substance found in Amesbury from the same batch?
This is yet to be established either way, with Mr Javid only saying he could not rule it out.

- Did the couple visit any of the same locations as the Skripals?
There is no evidence that they did. Mr Javid said: "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."

- Who was responsible for the Salisbury attack?
The UK government has pointed the finger squarely at the Russian government, an allegation the Kremlin denies.

- Has any individual been identified as a suspect in that case?
Not publicly. Police say their "complex" investigation remains ongoing.