This is actually a pretty good reference site for information about supplements etc.
Its american, but you can't have everything :)
http://ods.od.nih.gov/factsheets/VitaminD-QuickFacts/
You do not need a great deal of daily exposure to the sun for the body to manufacture the requisite amount of Vit.D.
It is however just about the only dietary supplement/ vitamin I might consider taking myself, especially if I lived in areas where for long periods there was little sunlight.
In the US, milk is routinely ( I think) fortified with Vitamin D, but not in the UK, although you can buy fortified food products containing Vit.D from stores like M&S