A metallic-green fly on Marsh Ragwort. I think it is probably a Lucilia, possibly L. caesar.
Edit: Further photo added.
No interactions present.
It's not possible to go to species from the photo...you need a better photo of bristles on legs...etc.
My Flickr photos...
I see the main colour as blue merging with green at the edges. Possible Blue bottle?
Lat/Lng: 55.4737, -3.2026
OS grid ref: NT240206