Vitamin D is vegetarian just like eggs and milk are.
But there are versions of vitamin D that are vegan. Almost all the plant milk companies use it.
I've never had Vimto or even heard of it but it seems to me that if they were going to spend money on adding Vitamin D - they might as well spend a little extra and kept it vegan.
They use D3 instead of D2 which is a shame. Vimto tastes fabulous and makes a most refreshing drink during the hot summer months. It's very popular esepcially in the Middle East.