Popular breakfast cereals including Rice Krispies, Kellogg's cornflakes and Cheerios contain vitamin D which is made from sheep's wool grease, it has emerged, meaning they are unsuitable for vegans.

It is feared that many of the UK's 550,000 vegans may have been eating vitamin D fortified cereals, as they contain no ingredients which are obviously derived from animals.

They are marked with a "suitable for vegetarians" logo, with no explicit warning that they are unsuitable for vegans.

Confusingly, other cereals which are suitable for vegans such as Nestle's Shredded Wheat, also carry a Vegetarian logo and not a Vegan logo.