Drug companies have been testing the spray - which is already available in the US as a homeopathic medication - in clinical trials and found that it reduced the average length of a cold from almost ten days to 36 hours..

However, specialists investigating the common cold warned that it was too early to tell if the treatment would be genuinely useful.

The spray - known as Zicam - is being developed by Gel-Tech, a joint venture between three US companies.

Promising results

"This initial clinical research showed that participants who used Zicam at the onset of symptoms significantly reduced the duration of their colds," said Dr Charles Hensley, head of research at Gel-Tech.

The researchers looked at 104 people who had suffered cold symptoms for up to 24 hours and gave them either Zicam or a dummy spray to use four times a day.

Those using the dummy spray suffered sneezing, runny noses and other symptoms for an average of 9.8 days compared with 1.5 days for the others.

The medicine had "no known side effects," was described as "soothing" and could be used by children as young as three, a company spokesman said.

Zinc has been used to tackle the common cold before, but while some studies have shown zinc lozenges to be effective, there have been problems developing a spray.

Tolerable formula

Professor Ron Eccles, head of the Common Cold Centre in Cardiff, said zinc may prevent viruses that cause colds from attacking cells.

Ron Eccles said zinc can block the virus

"Quite a bit of work has been done on zinc nasal sprays in the past, but most people have found them irritating," he told BBC News Online.

"So it's interesting that they've got a formulation that is well tolerated."

However, he said the results should be interpreted with caution.

"It's a first report, and obviously the company does have a commercial interest in it being good," he said.