I think you have Tree Bumblebees (B. hypnorum).
They frequently nest in Bird Boxes, but often also in house soffit boxes, eaves etc.
The standard fur colour pattern for them is Orangey brown thorax, black for most of the abdomen, and a white tail.
The thorax fur can vary from yellowish to chocolate brown.
Your photos fit this colour pattern.
Take a look at the discussion about them in the “Bumblebee Discussion” thread on this Forum - there is much info on them there.
Hi Clive, thanks for this. We thought they might have been, but wanted to check with people more knowledgable than us. I will definitely have a look at the other thread. Many thanks again Fluffy x