Mad dogs and Englishmen go out in the midday sun - and scientists now say it is good for them.

If the sun appears this bank holiday weekend, people should expose themselves for 10 to fifteen minutes without sunscreen, said Ann Webb, an ultraviolet radiation expert at the University of Manchester.

Sunlight helps the body produce vitamin D and Dr Webb said: "Our calculations have found that the best time to be out in the sun if you want to maximise vitamin D production and its benefits is midday.

"This is when there is more UVB radiation in the spectrum, which triggers vitamin D production in the skin."

She calculated that 10 to 15 minutes at noon is the optimum time for the average person in the UK to spend in the sun without sunscreen.

"You do not need to sunbathe to get your vitamin D and we are not advocating people do not protect themselves with sunscreen, but if you put sunscreen on before you step out of the house, you will not reap health benefits provided naturally by the sun."

Vitamin D promotes the absorption of calcium and phosphate from food, and is essential in the formation of bones and teeth. A deficiency leads to bones failing to grow and causes rickets in children and osteoporosis in adults.

Cancer Research UK said: "We recommend people stay out of the sun between the peak hours of 11 and 3.

"Fair-skinned people can burn in less than 30 minutes even on cloudy days and the danger is that you lose track of time."