[PeterD]

Originally Posted by JRsbugs

The black fly looks good for Polyporivora ornata but I would get expert opinion to be sure.

Diptera.info - Photo Albums: Polyporivora ornata (male) (1)

Last one should be Scathophaga stercoraria as it has black antennae.

Thank you Janet for your IDs and also the link to the diptera site. I have added it to my favourites and registered there.
Looking at the fly you have linked to, it seems to fit very well. When I have completed the registration process on that site I shall get someone there to confirm one way or the other as you have suggested.