Hi jeremiah,
The bee which has a noticeable 'm' shaped yellow collar is Bombus pratorum female or queen. I have seen workers until recently, the small amount of red on the tail tip can be worn and difficult to see but your bee looks too big for that.
The most likely one you saw is Bombus terrestris queen, I saw a large one today and they do visit Buddleja. The tail colour can be quite a small area and is very variable in colour, some having a very rich deep orange colour. Even though your pics are distant I can see a small area of the tail which is coloured in the second pic. The band on the abdomen can be dark and from a distance might not be seen.
I really can't think what else could fit.
