Apparently these are Spanish bluebells - the bells are all around the stem which means they stand upright, whereas English bluebells have all the bells on one side of the stem and so bend over. In England the Spanish bluebell is seen as an invasive species, threatening the native English bluebell - read more about this here, and about bluebells generally here on Wikipedia.
Did you know bluebells are part of the asparagus family ?From BBC Nature : Asparagus, bluebells and their relatives are a large and very diverse family of flowering plants, containing many genera and thousands of species. Members in this family can be found from the arid deserts of Mexico to damp British woodlands. The plants in this family range from the edible, such as the vegetable asparagus, to popular ornamentals such as the yucca and aspidistra. The large succulent Agave and the more delicate English bluebell are also included.