There is an interesting list to be seen on this link – the list gives due warnings about ones which may link to allergies or medical conditions. Further down the page is a list of books on the subject and also a few recipes for very well-known edible flowers. It gives a wider view of what can be grown on an allotment as edible crops.
It is worth growing edible flowers on the allotment where possible, both for culinary reasons and for the wildlife that will be attracted. It makes a change to grow crops which are not attractive just to slugs, snails, pigeons and sparrows.
But not every flower is edible. The are a group of common garden flowers which are ALL POISONOUS to a greater or lesser degree which should be especially avoided in the food production round. Sadly, the poisonous list includes some common and very attractive flowers which may be best avoided both on the allotment and in the garden if there are small children in the family. At least until they grow old enough to be told of the dangers and to be trusted to leave these flowers for the vase, the wildlife and the compost heap after flowering.