Hi Geoff, thanks for looking at my pics and for the suggestions. I'm getting much the same problems as you with Platycheirus, I spend hours looking and changing names then remove the species name altogether! I really should have a book, but the only way I think for me to get a chance of ID on the difficult ones is to get the expert to look on diptera.info, he is very good on Platycheirus, all syrphids in fact even if he had a rare day off for which he was very apologetic.
Sphaerophoria I think are difficult without a specimen, but I don't know if a few good close up angles would make it possible. Mostly they end up being called S. scripta but we should be aware that it may not be correct.
I do have a pic of the Pipiza showing the front tarsi, but it's distant. They look to be banded from what I can see. Again these are notoriously difficult from pics, I wish I had a better lens last year but I'm making up for it this year.
I'll upload the pic anyway as well as a few Eristalis which I'm sure of, others I need to be more sure of.