HONG KONG, Nov 28 (Reuters) - Physical barriers, such as regular handwashing and wearing masks, gloves and gowns, may be more effective than drugs to prevent the spread of respiratory viruses such as influenza and SARS, a study has found.

The findings, published in the British Medical Journal, came as Britain announced it was doubling its stockpile of antiviral medicines in preparation for any future flu pandemic.

Trawling through 51 studies, the researchers found that simple, low-cost physical measures should be given higher priority in national pandemic contingency plans.

"Mounting evidence suggests that the use of vaccines and antiviral drugs will be insufficient to interrupt the spread of influenza," they wrote in the report.

The 51 studies compared any intervention to prevent animal-to-human or human-to-human transmission of respiratory viruses, such as isolation, quarantine, social distancing, barriers, personal protection and hygiene, to doing nothing or to other types of intervention. They excluded vaccines and antiviral drugs.

They found that handwashing and wearing masks, gloves and gowns were effective individually in preventing the spread of respiratory viruses, and were even more effective when combined.

"This systematic review of available research does provide some important insights ... There is therefore a clear mandate to carry out further large trials to evaluate the best combinations," the international team of scientists wrote.

Another study, published in the Cochrane Library journal last month, found handwashing with just soap and water to be a simple and effective way to curb the spread of respiratory viruses, from everyday cold viruses to deadly pandemic strains.

Researchers have long warned that the world is due for another pandemic but they cannot say which strain will strike. The H5N1 avian flu virus that has killed more than 200 people globally since 2003 is considered a prime suspect. (Reporting by Tan Ee Lyn; editing by Roger Crabb)