Coalition forces face little danger if Iraq uses chemical or biological weapons against them, three UK experts believe.
By Alex Kirby
BBC News Online environment correspondent
They say the weapons would be largely ineffective against well-protected troops, if Iraq does possess them and decides to use them.
Several think the risk of similar attacks in Western cities is also fairly low.
But they believe American readiness to use non-lethal toxic agents like tear gas is dangerous.
The three are among the UK's leading scientists in the field, and were speaking at a briefing at the Royal Institution in London.
They are Alistair Hay, professor of environmental toxicology at Leeds University, Julian Perry Robinson, professor of science and technology policy research at the University of Sussex, and Brian Spratt, professor of molecular microbiology at Imperial College London.
Professor Hay said: "I'm far from clear whether Iraq would run the risk of losing what support it has by using CB weapons.
"I'm unconvinced it would use them - if it does possess them in useable form."
He said he would expect "minimal" coalition casualties if there were an Iraqi attack.
Professor Spratt said anthrax could be controlled on the battlefield by troops with suitable protection.
"It's more of a concern in places like the UK," he said. "And the release in the US showed agents like that are weapons of mass destruction, and of mass disruption."
Both sides in Iraq have gas protection
He said anthrax headed the list of biological threats. Next was plague, while smallpox was "of huge concern".
Professor Hay told BBC News Online: "You do have to take precautions against weapons like these.
"But if someone is going to use terror to spread panic in a city like London, there are far simpler ways.
"Explosives are much easier to use than CB weapons, which I'd put low down the list."
Professor Perry Robinson said the quantity of many agents needed for a successful attack could be huge.
"With VX gas, half a milligram is lethal," he said. "But the militarily significant amount you need on a battlefield is one billion lethal doses.
"You have to use a million doses to be sure of inflicting just one casualty - and that's about a tonne of VX.
Breaking the barriers
"Modern, well-maintained gas masks and suits give very good protection. And once the element of surprise has gone, the agent is effectively harmless."
What concerned him was the stated willingness of the US to use non-lethal toxic agents in battle.
Professor Perry Robinson said: "What we're really worried about is the long-term implications for our ability to manipulate chemicals.
Anthrax alert: Decontaminating US postal workers
"We can coerce and repress people by all sorts of chemical means that are opening up.
"And that's the worry. To see chemicals as weapons of mass destruction is to miss the point, because then you just think of lethality.
"We see them as terrorists' weapons, but their use against terrorists is becoming a big issue, like CS gas and fentanyl, used in the Moscow theatre siege.
"Once you admit non-lethal toxic agents in war - something specifically banned under the Chemical Weapons Convention - you are on a hard road.
"It leads to chemical weapons based on the targets' ethnicity or other factors, and results that would persist for generations."
The US Defence Secretary, Donald Rumsfeld, has asked President Bush to authorise the use in Iraq of riot control agents.
The US has shipped to the Gulf both CS gas and pepper spray, whose use the convention allows only in domestic civil disturbances.