Hand washing is the single most effective thing to do to reduce the spread of infectious diseases. Failing to sufficiently wash hands contributes to nearly 50 per cent of all food borne illness outbreaks, according to the U.S.Centers for Disease Control and Prevention.

Experts say it takes 15 to 20 seconds of vigorous hand washing with soap and water to effectively kill the germs which cause infections. Yet the study found that people washed their hands for, on average, only about six seconds. A third of people do not use soap when washing their hands and 10 per cent do not wash their hands at all.

Professor Borchgrevink's team observed hand washing in toilets in bars, restaurants and other public establishments.

Among the findings were that 15 per cent of men didn't wash their hands at all, compared with ? per cent of women and when they did wash their hands, only 50 per cent of men used soap, compared with 78 per cent of women. People were less likely to wash their hands if the sink was dirty and hand washing was more prevalent earlier in the day.

Professor Borchgrevink, who worked as a chef and restaurant manager before becoming a researcher, said the findings have implications for both consumers and those who operate restaurants and hotels.

He said: "Imagine you're a business owner and people come to your establishment and get a food borne illness because they didn't wash their hands — and then your reputation is on the line. You could lose your business. "