The density of flowers on the flower spike is a good guide to distinguish V. thapsus from V. virgatum and V. blattaria. Flowers and seed pods on V. thapsus are crowded together but are more widely spaced on the others.
No. Tbis is V. virgatum with green leaves and widely spaced flowers. I was suggesting the flower spike is an additional way of distinguishing the various species. See also my comments on virgatum/blattaria (click on the nearby sighting - I can't give you the sighting number until I go to my PC).