An anti-toxin that protects against ricin poisoning is to move into production for the first time.
It is the result of eight years of work by researchers at the Defence Science and Technology Laboratory based at Porton Down in Wiltshire.
The antidote can protect against death up to 24 hours after exposure, according to Dr Jane Holley from DSTL.
Security experts say ricin - roughly 1,000 times more toxic than cyanide - could be used in a bio-terror attack.
Dr Holley told BBC News: "In the past there has been lots of research carried out using different methods. But this is the first [anti-toxin] that has been moved into production.
The principal scientist in biomedical sciences at DSTL added: "It is anticipated that a product will be available for use in the next couple of years."
Ricin is extracted from castor beans, which are processed throughout the world to make castor oil. The toxin is part of the waste "mash" produced when castor oil is made.
It can cause harm if injected, swallowed or inhaled. A tiny quantity can be lethal, but the amount needed to kill depends on the route of administration.
A combination of pulmonary, liver, renal and immunological failure can lead to death, though people can recover from exposure.
The ricin-filled pellet that killed Georgi Markov was injected using an umbrella
In recent years, the perceived threat of bioterrorism has increased.
Although the anti-toxin developed at Porton Down was initially intended for use by the military, DSTL scientists are investigating its potential use in a civilian environment.
Production of the anti-toxin involves immunising sheep with an inactive form of ricin, which results in the production of antibodies. These are proteins used by the immune system to neutralise harmful substances.
The antibodies are then harvested from the sheep to produce a freeze-dried product. This is reconstituted with water for injection into the body.
Dr Holley said that although the anti-toxin is ready to be manufactured, full licensing is likely to take about five years.
Professor Alastair Hay, a toxicologist at the University of Leeds described ricin as "a very potent poison".
"Having an anti-toxin in the armoury would be very helpful for anyone who has to deal with possible ricin poisoning," he told BBC News.
Ricin was the poison used for the infamous murder of Bulgarian dissident Georgi Markov in September 1978.
Mr Markov, who was an avowed critic of Bulgaria's communist regime, was waiting at a bus stop near Waterloo Bridge, London, when a stranger jabbed him in the leg with an umbrella.
The rigged umbrella injected a tiny ricin-filled pellet into Mr Markov's calf. He was admitted to hospital that evening but died three days later.
Kamel Bourgass was convicted in 2005 of plotting to use poisons
In 2005, an Algerian man, Kamel Bourgass, was convicted of plotting to use poisons - including ricin - to cause disruption, fear or injury.
He was arrested after anti-terrorist squad officers found a suspected poisons laboratory in a north London flat in January 2003, though the toxin itself was not found.
There have also been incidents in the US; in 2004, an alert was triggered after tests identified ricin in a Senate office building mailroom.
The development of the ricin anti-toxin follows on from work to develop an "antidote" for poisoning with botulinum toxin.
"Although there had been small-scale batches of anti-toxins for botulinum available in hospitals, for military use we needed a large capability in case it was used as a biological weapon. We developed an anti-toxin against all seven 'serotypes' of botulinum toxin," Dr Holley explained.
Serotypes are structurally distinct forms of the toxin.
Dr Holley added: "This has been available for several years now, has been made to good manufacturing practice and is undergoing full licensing studies at the moment."
Research has also been carried out into a vaccine against ricin poisoning. While an anti-toxin works by mopping up the poison once it is in the body, a vaccine would prime the body for exposure to the agent.
Its effectiveness would depend in part on the period of time between administration of the vaccine and exposure to the agent.
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