No interactions present.
Looks a bit like Urophora cardui, although may not be this particular species?
Thanks. I know you can't reach a positive id based on a photo but it looks right and there's certainly a lot of Cirsium arvense near this site. Will look out for galls!
I believe there is an RESL handbook on Tephritidae which may help. This has keys and illustrations of wing patterns which are diagnostic for some species (though not all).
I've ordered my copy. Thanks
This is Urophora quadrifasciata, which has larvae developing in Common Knapweed. A pretty fly.
Entomologist and biological recorder
Lat/Lng: 52.725425502573, 0.30971199274063
OS grid ref: TF560166
Sown wildflower meadow about 10 years old