Confidence: It might be this.
Notes: Could this be Bombus lapidarius?
I've looked at the Field Guide to the Bumblebees of Great Britain & Ireland by Mike Edwards & Martin Jenner. I think the red tail is <50% of abdomen length and the wings don't appear to be dark-tinged as in Bombus rupestris.
Apologies that the photos are not as close as I would have liked but the bees were very active.
All advice very much appreciated.