Moderate exercise does not protect people against the flu in the same way that strenuous exercise can, according to a survey by the London School of Hygiene and Tropical Medicine.

The online Flu Survey, now in its fifth year, attempts to track details of peoples' symptoms in order to find patterns for flu contraction.

This year's data shows that 100 cases of flu per 1,000 people could be prevented by taking part in some form of vigorous exercise, categorised by the survey as running, fast cycling or competitive sports.

Dr Alma Adler of the London School of Hygiene and Tropical Medicine told the BBC that although these results are only preliminary, they are "consistent with findings from other conditions and really show the health benefits of exercise.”

Researchers also said this year's survey found some of the lowest reports of flu-like illness in recent years.

Over the winter flu season only 4.7 per cent of reports were positive for flu-like symptoms compared to 7.9 per cent last year.

Additionally, only 5 per cent of children reported symptoms this flu season compared with 7.9 per cent last year.