Just a thought, Mark. The tails seem rather orange for Bombus lapidarius so could they be cuckoos? Such as Bombus rupestris which takes over existing Bombus lapidarius nests.
You seem to have beaten me with that hoverfly, Victor. Possibly a Parasyrphus species? Or just occasionally the common Syrphus ribesii can have the abdomen bands broken in the middle.
Something different from my last sunny day. Tachina grossa. Looks like a one inch long bluebottle but it is a different species.
And another oddity, probably Sciara hemerobiodes