Some possible ways a person may survive a nerve agent attack

It is no surprise that Sergei and Yulia Skripal did not die immediately from a nerve agent attack, according to a security and chemical defence consultant.

Dan Kaszeta, who boasts 27 years' experience in the field, said there are potentially many "variables" about the impact of the Novichok nerve agent attack which left Mr Skripal, 66, and his daughter Yulia, 33, fighting for their lives in hospital after being found unconscious on a park bench in Salisbury on March 4.

He suggests that anyone who has ever tuned in to a Hollywood spy thriller and is now questioning why a nerve agent has failed to deliver a killer blow should understand that "the reality is that chemical warfare is not sexy, it can be quite boring and does not live up to the hype".

Mr Kaszeta - in an article on politics.co.uk - describes nerve agents as chemical substances that interfere with the chemistry of the human nervous system by binding with an enzyme called acetylcholinesterase.

Nerve agents are quick-acting if they are inhaled and this does not seem to be the case with the Skripals, he suggests.

If the Skripals became ill through contact that was made via the skin then "something that absorbs into the skin takes a long time", he points out.

Mr Kaszeta also notes there is "a human factor" which may have an impact.

He said: "We do not know the narrative of that afternoon in detail, for example Sergei - what did you touch and when did you touch it?"

Mr Kaszeta added that there are "some variables" such as whether they were wearing gloves or washed their hands, which could have weakened the potential dose.

Now that Ms Skripal in particular is known to be recovering and talking, her insight into what happened will be "extremely important", according to Mr Kaszeta.

He said: "It helps us pick out the narrative of what happened and when.

"Now that she is awake, she can help to build that timeline on what went on.

"When they were both unconscious there was a lot that had to be surmised but that is not now the case."

Mr Kaszeta said he is "not terribly surprised" about the Skripals' survival as they were treated and got competent medical care.

He described the idea that if you are in touch with a nerve agent you die as "folklore", adding "it is extremely important" to get medical care.

An important treatment could be the drug atropine, which works against the acetylcholine in the nervous system.

He said atropine is stocked in ambulances and hospitals for a number of uses, including overdoses and cardiac situations.

In his politics.co.uk article, he wrote: "In the case of Salisbury, atropine is specifically referenced in the hospital trust's publicly-available emergency plans. There's nothing odd or strange about atropine being available in Salisbury."

He pointed to the 1995 sarin attack on the Tokyo underground that killed 12 people and gas attacks in Syria as major incidents where many people survived.

Mr Kaszeta added that being in the middle of a war zone probably meant that victims in Syria were not able to get to modern medical care and those in Tokyo who did not survive were those who did not get treated soon enough.