Bees - Buff or Butch?

I have the most recent Cumbria Bumblebee Atlas in front of me and am trying to work out which bee this is out of the 21 recorded species. This one was enjoying the willow flowers at the sailing club in the sunshine and probably has only just come out of hibernation. It doesn’t help that I only have side views, but I think that it may be a female Vestal cuckoo bee.
 If so, that’s both interesting and disturbing because these deceptive insects parasitize, other bumblebee colonies, specifically Buff-tailed bumblebee colonies. Buff tails hatch out earliest of all the bumblebees in the year and by now will be rearing young. The Vestal thus has timed things just right to walk into the nest, kill the real queen and lay her own eggs for the workers to feed and rear.   
The reasons I think this might be a cuckoo are that she doesn't seem to be collecting pollen and I can't distinguish pollen baskets on her hind legs; she doesn’t need to work of course, as she relies on the host species workers. Vestal cuckoos also have very neat hair. You can see this one’s like a crew-cut – very butch - rather than a shaggy pile one, like the Buffs. You can see the shine of her strengthened thorax through the hairs – body armour to enable her to fight the resident queen. Her wings are dusky, and her tail incurved. If worker bees attempt to attack her initially, she can clamp them under her tail and sting them to death.
That’s quite a dark story for a Spring day!