One of the world's most deadly poisons is being used as a novel medicine to alleviate symptoms in some serious diseases.

Speaking at the British Association Festival of Science, doctors said that botox, as it is called, has completely revolutionised the treatment of muscle spasms.

Botox is the most powerful nerve toxin known to man. It comes from the bacterium that causes botulism - a very serious type of food poisoning.

But doctors are now using it to treat certain symptoms of illnesses like Parkinson's disease, multiple sclerosis and cerebral palsy.

Often patients suffering from these types of conditions appear to shake uncontrollably, because their muscles become over active and go into spasm.

Botox, which has been purified and then diluted, can be injected straight into the muscle, relieving the spasms. Professor Michael Barnes, from the University of Newscastle in the UK, is one of the leading specialists in this field of medicine.

He told the BBC: "I think revolutionised is not a too strong a word for the way it's helped people with muscle spasm and spasticity in particular. And I think we're going to see a lot more of it in the next few years, if it can help other long-term conditions."

According to Professor Barnes, the treatment is completely safe and there are no side effects.

Another potential use for botox is to relieve chronic back and neck pain - in particular, helping people injured in car accidents. This, the researchers say, would be particularly useful because far fewer doses would be needed compared with conventional drugs - the effect of botox can last quite a few weeks.

Botox has received much publicity recently as a cosmetic treatment for wrinkles.