BBC

“…..The name Novichok means “newcomer” in Russian, and applies to a group of advanced nerve agents developed by the Soviet Union in the 1970s and 1980s.

They were known as fourth-generation chemical weapons and were developed under a Soviet programme codenamed Foliant….

These nerve agents were designed to escape detection by international inspectors…..

One of the group of chemicals known as Novichoks – A-230 – is reportedly five to eight times more toxic than VX nerve agent…..

A number of variants of A-230 have been manufactured. One of these experimental chemicals – A-232 – was reportedly used by the Russian military as the basis for a chemical weapon known as Novichok-5.

Russia’s ambassador to the UK, Alexander Yakovenko, has suggested British authorities have identified the variant used in the Skripal attack as A-23…..

“Based on public sources, A-234 is one of the Novichok family of agents… Little is known about it but the symptoms track closely with those eyewitnesses attributed to Sergei and Yulia Skripal – as do other similar nerve agents…….

While some Novichok agents are liquids, others are thought to exist in solid form. This means they could be dispersed as an ultra-fine powder.

Some of the agents are also reported to be “binary weapons“, meaning the nerve agent is typically stored as two less toxic chemical ingredients that are easier to transport, handle and store.

When these are mixed, they react to produce the active toxic agent……..

Novichoks were designed to be more toxic than other chemical weapons, so some versions would begin to take effect rapidly – in the order of 30 seconds to two minutes.

The main route of exposure is likely to be through inhalation, though they could also be absorbed through the skin.

However, in powder form an agent might take longer to cause a reaction……

Novichok agents have similar effects to other nerve agents – they act by blocking messages from the nerves to the muscles, causing a collapse of many bodily functions.

Dr Mirzayanov told BBC Russian that the first sign to look out for was miosis, the excessive constriction of the pupils.

A larger dose could cause convulsions and interrupted breathing…..”