Bumble Bee with red tail - or a cuckoo bee?

Bumble Bee with red tail - or a cuckoo bee?

Observation - Bumble Bee with red tail - or a cuckoo bee? - UK and Ireland. Description: First thought was red-tailed bumble bee (B. lapidarius) but wings seem a bit dark and maybe no pollen basket - or is it just at the wrong angle? - so maybe B rupestris? Can't make up my mind!

First thought was red-tailed bumble bee (B. lapidarius) but wings seem a bit dark and maybe no pollen basket - or is it just at the wrong angle? - so maybe B rupestris? Can't make up my mind!